A zombie computer

Many people knew that a hacker can use a computer connected to internet for his illegal purposes. Such computers which are connected to the internet that obeys a hacker via a virus or trojan is called a zombie computer. The computer became a zombie when a virus or trojan gets installed the computer. There may be several such computers working simultaneously for a particular hacker. This makes it difficult to trace the hacker. Since the owner of the computer is unaware of this, the computer is known as zombies.
Zombies are generally used for sending spam emails and for the spreading of the trojans or computer viruses. This help the spammers not only to save their bandwidth cost but also to remain undetected. Certain hackers use zombies to commit click fraud against the sites displaying the pay per click advertisement. The hackers use the zombies for the Denial of Service (DoS) attack. Here the hacker sends unnecessary packets to the targeted website so that the legal users cannot access the website. The intense flooding can be easily found out and prevented, but the pulsating flooding remain unidentified for several months or years. The DoS attack is even done against the top sites like yahoo,ebay etc.
Network Intrusion-prevention systems (NIPS) are usually useful for preventing, detecting and blocking zombie computers.Computer users frequently perform backups and delete suspicious mail messages as preventive measures against infection.