Personal Firewall 3.1
The most common methods used by
The most common methods used by intruders to gain control of home
computers are briefly described below.
- Trojan horse programs
Trojan horse programs are a common way for intruders to trick you
(sometimes referred to as "social engineering") into installing "back
door" programs. These can allow intruders easy access to your computer
without your knowledge, change your system configurations, or infect
your computer with a computer virus.
- Back door and remote administration programs
On Windows computers, three tools commonly used by intruders to gain
remote access to your computer are BackOrifice, Netbus, and SubSeven.
These back door or remote administration programs, once installed,
allow other people to access and control your computer.
- Denial of service
Another form of attack is called a denial-of-service (DoS) attack.
This type of attack causes your computer to crash or to become so busy
processing data that you are unable to use it. It is important to note
that in addition to being the target of a DoS attack, it is possible
for your computer to be used as a participant in a denial-of-service
attack on another system.
- Being an intermediary for another attack
Intruders will frequently use compromised computers as launching pads
for attacking other systems. An example of this is how distributed
denial-of-service (DDoS) tools are used. The intruders install an
"agent" (frequently through a Trojan horse program) that runs on the
compromised computer awaiting further instructions. Then, when a
number of agents are running on different computers, a single
"handler" can instruct all of them to launch a denial-of-service
attack on another system. Thus, the end target of the attack is not
your own computer, but someone else’s -- your computer is just a
convenient tool in a larger attack.
- Unprotected Windows shares
Unprotected Windows networking shares can be exploited by intruders in
an automated way to place tools on large numbers of Windows-based
computers attached to the Internet. Because site security on the
Internet is interdependent, a compromised computer not only creates
problems for the computer's owner, but it is also a threat to other
sites on the Internet. The greater immediate risk to the Internet
community is the potentially large number of computers attached to the
Internet with unprotected Windows networking shares combined with
distributed attack tools.
Another threat includes malicious and destructive code, such as
viruses or worms, which leverage unprotected Windows networking shares
There is great potential for the emergence of other intruder tools
that leverage unprotected Windows networking shares on a widespread
There have been reports of problems with "mobile code" (e.g. Java,
developers write code that is executed by your web browser. Although
the code is generally useful, it can be used by intruders to gather
information (such as which web sites you visit) or to run malicious
ActiveX in your web browser.
- Cross-site scripting
A malicious web developer may attach a script to something sent to a
web site, such as a URL, an element in a form, or a database inquiry.
Later, when the web site responds to you, the malicious script is
transferred to your browser.
You can potentially expose your web browser to malicious scripts by
following links in web pages, email messages, or newsgroup postings
without knowing what they link to
using interactive forms on an untrustworthy site
viewing online discussion groups, forums, or other dynamically
generated pages where users can post text containing HTML tags
- Packet sniffing
A packet sniffer is a program that captures data from information
packets as they travel over the network. That data may include user
names, passwords, and proprietary information that travels over the
network in clear text. With perhaps hundreds or thousands of passwords
captured by the packet sniffer, intruders can launch widespread
attacks on systems. Installing a packet sniffer does not necessarily
require administrator-level access.
Relative to DSL and traditional dial-up users, cable modem users have
a higher risk of exposure to packet sniffers since entire
neighborhoods of cable modem users are effectively part of the same
LAN. A packet sniffer installed on any cable modem user's computer in
a neighborhood may be able to capture data transmitted by any other
cable modem in the same neighborhood.