A Trojan Horse is just one of many forms of malware.

Just under half of breaches involve some form of malware, according to Verizon. Malware, or malicious code, comes in many forms and can give hackers any number of capabilities, including complete control of an infected computer.

If a computer infected with malware is connected to a network, attackers can often access other connected systems and servers.

Unlike the old-school hacks that crashed people's computers, malware's job is to stay perfectly silent. The most sophisticated malware exists on a computer without its user ever knowing it's there.

Last updated July 29 2011: 5:11 AM ET
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