| Do you
have passwords, love letters, naughty pictures or
sensitive business information stored on your computer's
hard drive? If you have a continuous Internet connection
such as cable, xDSL, ISDN or other, you should know
that it's almost embarrassingly easy for a hacker
to break into a networked computer.
Once in, they can use your private
information any way they see fit. As well as getting
your personal documents, the hacker can damage
your system files or install software on your
disk that allows your computer to be used in Denial
of Service attacks and other destructive activities.
Similarly, the hacker can activate
your interior microphone or interior video recorder
without your knowledge. This lets them record
and distribute sound and video files of the conversations
and activities taking place in your work area.
How Hackers Do It
Every Internet-connected computer has a unique
set of identifying numbers called an IP address.
Using special software applications, hackers send
out probes over the Internet looking for live
IP addresses. If they locate your computer, they
look for "holes" or vulnerabilities that leave
your system insecure.
For example, a computer is likely
to have multiple applications (email, web browser,
etc.) running on the same IP address. Each application
is assigned a number called a "port" that uniquely
identifies that service on a computer. Ports that
allow an application to send or receive information
from the Net must be "open". In some unprotected
systems, even ports that are not in use have been
left open -- practically inviting attack! When
hackers discover an unprotected, open port, they
can use that opening to gain access to your system.
An unprotected broadband connection
is easiest to hack because both the connection
and the IP address remain constant. If a hacker
or a "script kiddie" finds your computer once,
they can readily find it again. (Script kiddie
is a derogatory name used by professional hackers
to describe simple scripts used by young and inexperienced
The threat is less severe for persons
connecting to the Internet via dial-up modems.
Dial-ups usually connect with a different IP address
each log-on. Therefore, if hackers have found
a system once, the changing IP address will make
it difficult (not impossible) to find it again.
However, if a trojan horse or back
door program has been installed on a system, the
trojan horse could "phone home" with the IP address
each time an Internet connection is made.
Back door programs allow remote
users to control a system without the owner's
knowledge. They are installed on computers by
hackers, or sometimes come secretly bundled with
software applications that the user installs.
Well-known back door programs for Windows computers
include BackOriface, NetBus and SubSeven.
Your First Level of Security Firewalls are software
applications or hardware devises that you install
on your system. They are designed to prevent unauthorized
access to or from a private network that is connected
to the Internet. When a firewall is installed,
all incoming or outgoing messages pass through
the firewall. Those that do not meet the specified
security criteria are blocked. Most home firewalls
are software applications.
How Firewalls Work
There are various types of firewalls, and they
work through different processes. However, the
following is true for most of the home or personal
firewall software that is used today.
Information over the Internet is
sent in "packets" of data. These packets travel
from a source machine to a destination machine
-- which could be two feet away or two continents
away. Each packet of data contains the IP address
and port number of the originating machine.
The firewall software inspects
every packet of data that arrives at the computer
-- BEFORE that data is allowed entry into the
system and before it connects with an "open" port.
The beauty of a firewall lies in its ability to
be selective about what it accepts and what it
The firewall has the ability to
refuse any suspect data. If the incoming data
is ignored and not allowed in, that port will
effectively disappear on the Internet and hackers
cannot find it or connect through it. In other
words, instead of receiving a signal that a port
is open, the hackers receive nothing back and
have no way of connecting.
Several firewall applications are
available to the small business operator or the
home computer user. Before changing firewalls
or installing one for the first time, it's wise
to check out the comparative testing that has
been done on these applications.
Persons already running a firewall
could test it's effectiveness by trying the Shields
and Ports test available at Gibson's Research
Corporation (GRC) web site, or by downloading
and running the LeakTest software available on
site at http://www.grc.com.
GRC's Steve Gibson has some surprising
test results posted in conjunction with LeakTest's
personal firewall scoreboard at http://grc.com/lt/scoreboard.htm.
The best-rated one is free. Not only did Zone
Lab's Zone Alarm (http://www.zonelabs.com) score
best in Gibson's testing, but the firewall has
been recognized for excellence by CNET, PC World,
PC Magazine and Home Office Computing.
Other well-known firewalls include
McAfee firewall at www.mcafee.com, Sygate Personal
FW at www.sygate.com, Symantec/Norton at www.symantec.com
and Tiny Personal FW at www.tinysoftware.com Now,
the bad news.
A firewall protects you from open
ports, but it does not protect you from data coming
and going through ports that you allow. Malicious
code can invade your system from email attachments
or by visiting a hostile web site. And remember
-- even well trusted web sites can suddenly be
hostile if hackers have added malicious code without
the site administrator's knowledge.
Test your security against malicious
code at Finjan Software's web site. Many of you
will be dismayed to find that your supposedly
secure system is vulnerable.
Malicious code blocking software such as Finjan's
Surf n' Guard analyzes incoming data and decides
whether the code could be harmful. ZDNet recommends
that code-blocking software be used in addition
to firewall and your antivirus software. Too Late?
What if you think you've been hacked?
Call your computer guru to help,
or check out the information at sites like HackFix.
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