Zombie Computers

A zombie computer/PC is a computer that has been infected with malicious software that can be used by the attacker to send spam or for DOS (Denial of service) attacks or to spread viruses. The term zombie arises from the fact that the person using the PC has no idea that the machine is being used.

Zombie computers are also called bots ( short for robots) and usually they are part of a network of compromised computers called a botnet. Botnets consisting of over 100,000 PCs have been uncovered. In fact botnets are actually traded over the Internet by spammers and the trade  has become an industry of its own.

Zombie computers are typically infected by Trojan horse software. A Trojan horse is a piece of software that the user believes does one thing but in fact does another. Even though Trojan horses cannot spread themselves they can be and often are spread by viruses (Sobig was he first virus to do this) and worms.

Are You Infected?

Even though virus checkers can and do detect some Trojan horses they offer only limited protection and limited removal capabilities. Therefore do not rely on anti-virus software alone but use a anti-Trojan horse program as well.

Even without anti-Trojan software there are several tell tell signs to look for. They are:

• Internet activity when you aren't yourself accessing the Internet

• Slow machine response.

• Disabled virus checker

• Unable to update virus checker

 There are three essential tools you should have and run regularly:

• Anti-Virus program

• Anti-Trojan Program

• Spyware detector

You should also never operate your computer on a network without a firewall. If you have only one machine that is connected to the internet via modem/DSL/Wireless then this machine should be equipped with a personal firewall!

Be aware that the software tools aren't infallible. Even if you have commercial tools it is often useful to also use free ones now and again as they may detect problems that the others didn't.

Cleaning your Machine

If you suspect an infection or your virus checker reports an infection then you need to clean it. Cleaning a machine is an iterative process and can take time.

 See Killing Zombies and Killing Spam Zombies Made Easy for more help.

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