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COMPUTER SECURITY
Lock out the bad guys
with a firewall
by Greg Swain
If you connect to the Internet, you need a firewall. Here’s
a quick rundown on three very effective firewalls:
ZoneAlarm, Sygate Personal Firewall & Tiny Personal
Firewall. They’re all free for personal use so there’s no
excuse for not taking action to protect yourself.
C
ONNECTING A COMPUTER to
the Internet without a firewall is
like leaving a car unlocked with the
keys in the ignition. Without a firewall, your PC can easily be hacked
and sensitive data stolen. In addition,
a cracker (or Internet vandal) could
damage the operating system or use
your machine to launch further attacks against other PCs connected to
the Internet.
Users with broadband connections,
such as cable modems and ADSL,
make particularly juicy targets. There
are a couple of reasons for this.
First, every computer connected
to the Internet must have a unique IP
(Internet Protocol) address and broad
band users usually either have a fixed
address or one that is assigned for very
long periods of time (ie, a “leased”
IP address). That makes it easy for
a cracker to repeatedly return to the
same computer and wreak further
mischief.
Second, users of broadband connections are more likely to be connected to the Internet for very long
periods, if not permanently. That,
plus the high-speed nature of the
connection, means that crackers are
more likely to zero in on users with
cable modems or ADSL.
By contrast, if you access the Inter
net via a dial-up connection, your PC
receives a different IP address each
time it makes a connection. This makes
it more of a moving target and, of
course, the connection is much slower so it’s less attractive for launching
denial of service attacks.
But that still doesn’t make you
safe – not by a long shot. Once you’re
connected, an unprotected computer
can quickly be “spotted” by a cracker
using a software tool called a “port
scanner”. This allows the cracker to
automatically portscan vast blocks of
IP addresses to find out what which
services are “listening” for a connection. A PC has some 65,535 ports (basi
cally data pathways) and if they are
left open, an intruder can gain access.
Of course, some ports are reserved
for specific functions. For example,
a web server communicates via port
80, FTP via port 21, incoming email
via port 110 and outgoing email via
port 25.
So be warned – an unprotected com-
Don’t Let The Firewall Nag You!
Once you’ve set up all the rules
for your firewall, you don’t want
it continually nagging you each
time it encounters an unknown
data packet. The way around this
is to turn off the alert notifications.
Here’s how:
(1) In ZoneAlarm, go to the Alerts
panel and clear the box next to
“Show the alert popup window”.
(2) In Sygate Personal Firewall,
16 Silicon Chip
click Tools, Options and check
the box next to “Hide notification
messages”.
(3) In Tiny Personal Firewall, click
the Advanced tab and clear the
box next to “Ask for action when
no rule is found”.
If you later find that the firewall
blocks something that it shouldn’t
you can quickly re-enable the alert
messages, create the new rules
then disable the messages again.
The log files can also help you sort
out any problems.
Finally, a tip – if your computer
automatically dials out each time
it is booted after a firewall has
been installed, find and uncheck
the “Check For New Version” or
“Check For Update” (or similar)
option buried in the firewall setup
menus.
www.siliconchip.com.au
puter is wide open and that applies
even if you use a dial-up connection,
since you can be spotted in just a few
minutes. And if you’re on a network
with file and printer sharing enabled
and bound to the Internet adapt
er,
you’re really asking for trouble.
Protecting yourself
So how do you protect your PC from
unwelcome visitors? The answer is to
install a firewall. This can either be
a hardware device that sits between
your PC and the Internet or a dedicated
piece of software.
The most basic software firewalls
simply function as port blockers; ie,
they close unused ports to prevent
unauthorised access. This is the type
of firewall that’s now incorporated into
Windows XP.
More sophisticated firewalls such as
ZoneAlarm, Sygate Personal Firewall
and Tiny Personal Firewall not only
close unused ports but also filter and
inspect the TCP/IP network packets as
they pass across the firewall interface
(this technique is called “Stateful Inspection”). Unwanted or unauthorised
packets are then blocked and logged,
according to a set of rules built into
the firewall. This not only allows them
to block attempted intrusions but also
prevents certain applications such
as Trojan horses and spyware from
communicating with the Internet from
your computer.
A “Trojan horse”, by the way, is
a program that’s smuggled into your
computer (either via email or when
you download from the web) to perform various nefarious activities.
Most firewalls (including these
three) can also selectively block other
PCs on a local network from having
access to your machine. That’s a
worthwhile feature if you want to keep
certain people in an office network
from prying on sensitive data.
Keeping Trojans at bay
A feature of all three firewalls is that
they create what are known as “MD5
signatures”. Initially, these firewalls
have to “learn” which applications
have Internet access. These applica
tions typically include web browsers,
FTP and email clients, plus other utilities (eg, Windows Update).
Each time a new application is
Don’t Take Security
For Granted
For the home user, the firewalls
described here should make for a fairly
secure system – provided they are properly
set up. Just keep them up-to-date and keep
an eye on the log files for any suspicious
activity and you should be OK.
However, we don’t offer any guarantees
– the net is not a safe place. If security is
vital, be sure to seek expert help in setting
up a firewall. Don’t just rely on the advice
in this article.
granted Internet access, the firewall
creates an MD5 signature (basically
a 128-bit algorithm) for that application. This signature is then stored and
compared with the signature generated
each time the application attempts to
bind to a particular port. If the signatures match, then access is permitted.
This technique effectively blocks
Trojan horse applications on your
computer from accessing the Internet,
since it prevents application “spoofing” –ie, where a Trojan attempts to
disguise itself as a valid application.
If the Trojan does attempt access, its
MD5 signature will be invalid and it
will be blocked.
A look at ZoneAlarm 2.6.362
Z
oneAlarm
is easy to install and
operate. It comes in two versions:
(1) ZoneAlarm 2.6.362 (the latest version at the time of writing) which is
freeware; and (2) ZoneAlarm Pro 3.0
which is a retail version costing about
$US40. The Pro version adds a few
extra features over the freeware version, including Internet ad blocking,
cookie control, full compatibility with
ICS (Internet Connection Sharing) and
the ability to block some 36 different
email worms (Mailsafe).
For personal use, the freeware
version should be sufficient. You can
download it from www.zonelabs.com
or from any one of a number of other
sites but make sure you get the latest
version.
When you launch ZoneAlarm (it’s
configured by default to automatically load at startup), the program
places a small icon in your system
tray and this also indicates incoming
and outgoing traffic. To configure the
program, you simply decide what
www.siliconchip.com.au
level of security you want
for your local network and
Internet zones. The choices
are Low, Medium and High
and are independently set
by dragging the two sliders.
The window text explains what the settings
mean. For a standalone
com
puter, you will want
to set the Internet zone to
High but this will have to
reduced to Medium (which
presumably weakens security) if you use Internet
Connection Sharing.
The “High” setting is generally preferable because
it places the machine into
Fig.1: ZoneAlarm offers independent security
stealth mode. This makes
settings for the local network and the Internet.
all ports not in use by an
application appear invisible to the Internet. By contrast, the Either setting blocks all Internet ac“Medium” setting blocks port access cess to Windows services and to file
but still leaves them visible, so it’s not
and printer shares, a very necessary
as good from a security viewpoint.
security feature.
June 2002 17
COMPUTER SECURITY continued . . .
Fig.2: ZoneAlarm initially pops up
frequent alerts until it “learns” which
programs have access to the Internet.
Fig.3: clicking the Advanced tab lets
you add machines to your local zone
but don’t choose the PPP adapter.
The Local zone can be set to “High”
for a standalone com
puter but the
“Medium” setting will be necessary if
you want other local machines to have
access to file and printer shares. Clicking the “Advanced” tab then takes you
to the “Local Zone Properties” dialog.
This is where you add “trusted” computers (eg, PCs on a local area network)
to your Local Zone.
The “Adapter Subnets” are created and automatically main
tained
by ZoneAlarm. You only have to
decide whether to check or uncheck
the entries. For example, checking
the Ether
net Adapter entry (under
Adapter Subnets) enables access for all
machines on the local network. Alternatively, you can leave this unchecked
and simply specify the IP addresses for
individual computers (or an IP address
range) to add an additional entry to
the “Other computers” section. Those
machines not covered by an IP address
(or address range) will then be blocked
by the firewall.
Initially, ZoneAlarm displays frequent alert panels and you have to
teach ZoneAlarm which applications
are allowed access to the Internet.
These applications typically include
your web browser, email client (eg,
Outlook Express) and any other Inter
net applications (eg, ICQ).
Basically, an alert panel pops up
when ever an application requests
access. You can choose to always block
access for that program, allow access
on a once-only basis or always allow
access. By this means, ZoneAlarm
quickly “learns” which programs can
have access and which ones to block
and the alerts all cease.
As well as blocking Trojans, this
feature is also very effective when it
comes to preventing “spyware” programs from contacting Internet-based
servers without your permission.
Other features of ZoneAlarm include an Internet lock and “Mailsafe.”
Sygate Personal Firewall
L
IKE ZoneAlarm, Sygate Personal Firewall 5.0 makes your computer invisible to the Internet by closing
all unused ports.
It also filters and inspects incoming
and outgoing traffic using rule-based
policies and can be configured to
allow Internet access for trusted applications, plus selective access for
18 Silicon Chip
computers on a local network.
Once again, there are two flavours –a
freeware version for personal use and
a fully-featured “Pro” version. Both
versions now offer full support for
Internet Connection Sharing, unlike
the previous 4.2 version.
During installation, Sygate Personal Firewall automatically discovers
Fig.4: the Programs tab shows which
applications have been granted access
to the Internet and to the Local Zone.
You can also change the settings here,
to grant or deny access.
Fig.5: placing the ZoneAlarm Desk
Band on the taskbar gives you fast
access to the various functions.
Clicking on the lock immediately
blocks all Internet activity, or you can
set it to block all Internet traffic after a
period of inactivity or when the screen
saver activates. You can also give certain programs the right to bypass the
lock (eg, if you want to check for email
at regular intervals).
The MailSafe feature scans all
incoming email attachments and
quarantines any .vbs (ie, Visual Basic
script) files by changing the extension
to .zlx (“x” can be either a letter or a
number). If you then try to open such
attachments, ZoneAlarm pops up a
dialog warning of the dangers of VB
scripts and giving you an opportunity
to back out.
the local area network and the ICS
Manager and creates the rules necessary to allow Internet Connection
Sharing. As with ZoneAlarm, it can
be automatically configured to load at
startup and (optionally) place an icon
in the System Tray. This icon flashes
red if an intrusion attempt is detected
and you can double-click it to open
the main console, before clicking the
Logs button to review the security log.
Alternatively, right-clicking the tray
www.siliconchip.com.au
Testing Your Firewall
Once you have a firewall installed,
you’ll want to test its effectiveness.
There are several web sites on the
Internet that allow you to do just that.
These commonly do port scans and
test for other vulnerabilities, and
some can even scan for the presence
of known Trojans.
Of these, perhaps the best known
sites are PC Flank at http://www.
pcflank.com and Steve Gibson’s
ShieldsUp site http://www.grc.com
In addition, Sygate has a test site
at http://scan/sygatetech.com and
you are automatically connected to
this when you click the Test button
in Sygate Personal Firewall.
However, there are some situations in which the tests from
these sites are rendered inaccurate. For example, if you use a
proxy server, it’s the proxy server
(eg, at your ISP) that could end
up being scanned – not your
local machine with the fire
w all.
That’s because it’s necessary for
the test site to accurately determine
your machine’s IP address before
running the tests and it’s often the
proxy’s IP address that it recognises
instead.
For example, the ShieldsUp site
at www.grc.com has a tendency to
recognise the proxy’s IP but this is
easily overcome by down
loading
a small utility called “IP Agent”.
Running this utility then sends the
machine’s correct IP address to the
ShieldsUp test site, after which you
can run the security checks.
The Sygate test site also has a
habit of recognising the IP of the
proxy server. In some cases, you
may be able to get around the problem by disabling the proxy server
settings in your web browser but
that depends on your Internet Service Provider – disabling the proxy
settings can sometimes prevent
web access!
By contrast, in the tests we ran,
the PC Flank site accurately determined the IP address of the local
machine, despite the use of a proxy
server. This site has several tests
that you can run, including: Quick
Test, Stealth Test, Browser Test
(checks browser security), Trojans
Test, Advanced Port Scanner and
Exploits Test.
Testing a firewall that’s on a client
machine that accesses the Internet
through a gateway (eg, via a PC with
Internet Connection Sharing) also
poses problems, since private IP
addresses aren’t recognised by the
Internet. As before, the results of any
web-based port scans and security
checks will be misleading since it’s
either the gateway machine of the
proxy server that will be scanned
by the test site
icon gives you quick access to all the
features of the firewall.
Security levels
There are three security levels –
Block All, Normal and Allow All – and
you can also click the “Block All”
button on the toolbar to immediately
block all Internet access. This is similar to the lock feature in ZoneAlarm.
The “Options” dialog box (found
under the Tools menu) provides various configuration and local networking options, while the “Advanced
Rules” dialog lets you create your own
firewall rules based on IP numbers,
port numbers and scheduling.
Fortunately, if you’re a complete
novice, you don’t have to worry about
any of this. Sygate Personal Firewall
is all set to go immediately following
installation. All you have to do is
answer the alerts it pops up when
you first start using it, to tell it which
applications should be granted Inter
net access.
As with ZoneAlarm, Sygate Personal Firewall then uses your answers
to create the access rules, so that the
alerts cease after a short period of
initial use.
Clicking the “Applications” button
on the toolbar brings up the Applicawww.siliconchip.com.au
Fig.7: you can quickly
gain access to Sygate
Personal Firewall’s
main functions by
right-clicking its icon in
the System Tray.
Fig.6: Sygate Personal Firewall 5.0 has an easyto-use interface that displays network traffic
and lists running applications. Right-clicking an
application lets you change its access status.
Fig.8: like ZoneAlarm, Sygate
Personal Firewall
“learns” which
applications have
Internet access.
June 2002 19
Fig.9: setting up local network and file
and printer sharing rights is a “no-brainer” in Sygate Personal Firewall.
Fig.10: the Advanced Rule Settings let
you specify access rights for certain IP
addresses, ports and protocols.
Fig.11: in this case, the firewall is
blocking a computer on the local network with an IP of 192.168.0.20.
tions list. You can change each application’s access status by right-clicking
it and choosing either Allow, Ask or
Block from the drop-down menu.
port scans and other security scans
but can also scan for the presence of
Trojans.
Note however, that Internet test
sites do not always give accurate results if you are using a proxy server
or are connected to the Internet via
a gateway (eg, using ICS) – see the
“Testing Your Firewall” panel for
further details.
Finally, Sygate Personal Firewall
features password protection. This
is designed to prevent your security
settings from being changed by other
users of the machine. And like Zone
Alarm, it can be set to block all Internet
traffic while the screen saver is active.
Tracing attacks
Fig.12: this dialog box lets you quickly
change Internet access rights for various applications.
A neat feature of Sygate Personal
Firewall is its ability to trace the path
of an attempted intrusion. However,
you can normally only trace the source
of an attack back to the router used by
the hacker to launch the attack, not the
hacker’s computer itself.
Finally, the Test button on the main
console logs you onto Sygate’s test site,
so that the effectiveness of the firewall
can be checked. This not only provides
Tiny Personal Firewall
L
AST BUT NOT LEAST, there’s
Tiny Personal Firewall. Let’s call
it TPF for short.
As with the previous two firewalls,
it’s best to fire up all your Internet
applications when you first install
TPF so that it can learn the ropes.
TPF then creates filter rules based on
your responses to the alerts it throws
up (you can customise these rules if
necessary).
TPF’s administration utility is
launched by double-clicking the icon
in the System Tray and is, initially at
least, disarmingly simple in appearance. The level of protection is set
using the 3-position slider control.
You can choose to cut off all network
activity (top position), permit network
activity according to the rules that
have been set (centre position) or allow
all network activity (bottom).
The medium security (centre) posi20 Silicon Chip
tion is the default level and
is necessary if you want
Internet access but want
to keep the firewall rules
in place (the top maximum
security setting blocks
everything, including Internet access). TPF provides a
few pre-defined filter rules
and the user is prompted
to set up a new filter rule
(permit or deny) each time
an unknown data packet is
encountered.
Clicking the Advanced
Fig.13: Tiny Personal Firewall’s interface is distab launches the Firewall
armingly simple at first glance.
Configura
tion menu and
opens up a whole new
world. This initially displays the Filter for individual filter rules if necessary.
Rules dialog, which lists all the rules However, you will need to have a
that have been created. You can then reasonable understanding of TCP/IP
edit, add or delete rules, change the
and port addressing to do this if you
rule order and even set time frames intend to create the rules from scratch.
www.siliconchip.com.au
Alternatively, if you don’t know
how to create the rules, you can let the
wizard do it for you each time you attempt to access a resource or browse to
a network share from another machine.
All you have to do is make sure that
the box next to “Ask for action when
no rule is found” is checked and follow
the bouncing ball to create the rules
from the alerts that pop up.
The other tabs on the Firewall
Configuration control panel (Microsoft Networking, Miscellaneous &
Application’s MD5) let you set up
local area networking options, trusted
address groups and logging options.
There’s also an “Is running on Internet
gateway” option that you can check
(under Miscellaneous). This feature is
apparently designed to make TPF work
with Internet Connection Sharing but I
couldn’t make it work on the two ICS
gateway machines I tested it on.
With TPF installed on a gateway
machine, I was unable to browse
the Internet from any of the client
machines – even with the firewall
disabled (or completely shut down
for that matter). Full browsing rights
were immediately restored when TPF
was uninstalled, however.
But don’t let this put you off TPF.
If you don’t plan to run this firewall
with Internet Connection Sharing, it
really doesn’t matter.
Which One Should You Choose?
Any of the three will do the job
quite nicely but if you’re a rank beginner, go for ZoneAlarm or Sygate
Personal Firewall. They are easy to
set up and you don’t have to learn
about ports and network protocols.
Those of a more technical bent
might prefer Tiny Personal Firewall.
It’s more flexible that the other two
and allows you to create and tightly
edit your own packet-filtering rules
– provided you have the know-how,
of course. Alternatively, you can let
the wizard create the rules for you
and then edit them afterwards.
Our advice is to choose the firewall that best suits your needs and
stick with it. But what ever you do,
don’t install multiple firewalls on
your PC or you’ll get all sorts of
foul-ups. And that applies even if
you have only one firewall running.
For example, having both Sygate
Personal Firewall and Tiny Personal
Firewall installed (but not running)
prevented both Internet and email
access with ZoneAlarm set for
high Internet security. Uninstalling
both SPF and TPF restored normal
operation.
Which one was causing the conflict? We didn’t bother to investigate
but it does indicate the sorts of
problems that can occur if you install
multiple firewalls. Don’t do it.
If you do want to try a different
firewall, uninstall the previous fire
wall first.
Filtering the local network
One very nice feature about TPF is
that it detects if there is a local area
network as soon as the machine is
rebooted after installation. The user
is then prompted to permit or deny
the network traffic. If it’s permitted,
then the LAN’s all set to go without
any further action from you.
By default, TPF sets up a “Trusted
address Group” for your LAN and
displays this under the Microsoft
Networking tab. This means that
if the machines on the LAN have
192.168.0.x IP ad
dresses (where x
is a number between 1 and 254 and
is different for each machine), then
TPF sets up a trusted address group
of 192.268.0.0/255.255.255.0.
This rule simply allows all machines on the 192.168.0.x network
to access shared resources on the
machine with the firewall.
Alternatively, by modifying the
Trusted Address Group, you can
restrict access to certain machines
only. For example, changing the trustwww.siliconchip.com.au
Fig.14: Tiny Personal Firewall initially displays frequent outgoing and incoming
connection alerts until it learns the ropes. The incoming alert here is from a
machine on the local network.
Fig.15: clicking the Advanced button in Fig.13 brings up this dialog which
shows all the current filter rules. You can add, edit or delete rules as necessary.
June 2002 21
filter rules yourself if you wanted to
share resources. We’ll show you how
to do that next month.
Living by the rules
One thing that’s important to remember here is that the rules set up
under Microsoft Networking override
any Filter Rules that you may create.
This means that it’s futile creating
separate Filter Rules to block certain
IP addresses (as in Fig.17) if they have
already been granted access under
Microsoft Networking.
In short, the rules listed under
Microsoft Networking will win out
every time.
If you wish to create your own Filter
Rules for the local network, make sure
that they will not be overridden by the
Microsoft Networking rules. In some
cases, it may be easier to disable the
Microsoft Networking rules altogether
(just clear the top check box).
Fig.16 (above): the Microsoft Networking section makes it easy to
grant or deny access for machines
on the local network. Note that any
settings here take precedence over
the filter rules.
Top-down rule order
Fig.17(right): the Filter Rules dialog
is very flexible and lets you create
rules based on protocol, packet
direction, ports and application.
You can even set up scheduling and
logging from here.
ed address group to 192.168.0.0
-192.168.0.10 re
stricts access to
machines with IP addresses in
this range. Machines with an
IP of 192.168.0.11 or higher are
blocked.
If you’re not on a local network, just
check “For Microsoft Networking Use
These Rules Instead Of Filter Rules”
and clear all other check boxes under
the Microsoft Networking tab. This
simple step prevents your computer
from being identified by machines on
an external network and denies access to any shared resources (not that
you should have any for a standalone
machine).
Earlier versions of TPF did not include the “Microsoft Networking” tab,
which meant that you had to set up the
Firewall Downloads
Firewall
Operating System
Sygate Personal
Firewall 5.0
Ti ny Personal Firewall
2.0.15
Windows 95/98/Me
Windows NT/2000/XP
Windows 95/98/Me
Windows NT/2000/XP
Windows 95/98/Me
Windows NT/2000/XP
Lavasoft Ad-aware
5.71
Windows 95/98/Me
Windows NT/2000/XP
ZoneAl arm 2.6.362
File Size
Download Site
2.92MB
www.zonelabs.com
4.74MB
www.sygate.com
1.42MB
www.tinysoftware.com
Spyware Checking Software
22 Silicon Chip
0.87MB
www.l avasoftusa.com
Another thing that’s important to
remember is that the Filter Rules operate in a “top-down” order. In other
words, filter entries at the top of the
table take precedence over entries
lower down.
This works as follows: let’s say that
you create a rule that allows access
for machines with IP addresses from
192.168.0.1 to 192.168.0.20 but then
have a rule further down that blocks
access for 192.168.0.10 only. Guess
what? – 192.168.0.10 will still have
access through the firewall since the
top rule “clobbers” the rule further
down.
Once permission for something has
been granted (or denied), you cannot
change it with a rule further down
the list.
The answer in this case is to move
the “blocking” rule up the list, so that
it is above the other rule. The blocking
rule then blocks 192.168.0.10, with the
following rule then allowing access for
the remaining machines.
That said, you wouldn’t normally
block access for individual machines
on a local network by creating separate
Filter Rules. Instead, it’s far easier
to block access by leaving the relevant IP addresses out of the Trusted
Address Group under the Microsoft
Networking tab.
We’ll take a closer look at creating
your own rules for Tiny Personal Firewall in next month’s issue.
www.siliconchip.com.au
A Few Basic Security Measures
Here are a few other security
measures that you can take to
protect your PC, whether you run a
firewall or not.
(1) Make sure that “File And
Printer Sharing For Microsoft Net
works” and “Client For Microsoft
Networks” are NOT bound to your
Internet adapter (note: this advice
applies whether you are on a local
network on not).
For example, if you use a modem to connect to the Internet, you
should unbind these services from
your Dial-Up Adapter. To do this,
right-click My Network Places (or
Network Neighborhood), select the
TCP/IP entry for the Dial-Up Adpater,
click Properties, click the Binding tab
and clear the check boxes.
(2) If you don’t require Internet access for any other machines on the
network, consider using NetBEUI as
your networking protocol for file and
printer sharing. TCP/IP can then be
removed from these other machines
altogether, thus effectively closing
NetBIOS ports 137-139.
Both TCP/IP and NetBEUI will be
required on the Internet machine but
make sure that TCP/IP is bound only
to your Internet adapter.
If you’re not running a network,
remove “Client for Micro
soft Networks” from your PC entirely.
(3) Visit Steve Gibson’s ShieldsUp site at www.grc.com for lots of
good advice on security measures.
(4) Check the Microsoft Update
Fig.18: make
sure that
Client for
Microsoft
Networks
and File
and Printer
Sharing are
not bound to
your Internet
adapter.
site regularly and install any critical
updates that involve security.
(5) Install a “spychecker” program
such as Ad-aware from Lava
soft.
This can detect and remove any
“spyware” and “adware” programs
that have snuck in.
Ad-aware is a free utility from
www.lavasoftusa.com but be sure
to regularly update its signature file
(called “reflist.sig”). A related utility
– refupdate.exe – can do this for you
automatically.
(6) Use the PCFlank site at http://
pcflank.com to scan your machine
for Trojans. You should also use
this site (or one of the other test
sites) to scan for open ports and
to test the effectiveness of your
firewall.
(7) Use a good anti-virus program
and regularly update its virus definitions file.
(8) Don’t run email attachments
unless they are from a trusted source,
they have been virus checked and
you know what they are.
SC
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For Technical Details and Professional Pricing Contact
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Buy a 1- or 2-year subscription to
SILICON CHIP and we’ll mail you a free
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can choose “Electronics Testbench”.
Fig.19: it’s a good idea to install a “spyware” checking utility such as Lavasoft’s Ad-aware but be sure to keep its signature file up-to-date.
www.siliconchip.com.au
Subscribe now by using the handy order
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June 2002 23
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