Taked from Maximum PC, January 2009 Edition

A computer virus is a piece of software or code capable of reproducing itself and spreading to others systems, but the term is often used to describe a multitude of threats.  The effects of malware can range from mildly annoying to completely debilitating, sometimes costing corporations thousands of dollars in downtime and manpower to heal the outbreak.  Let’s have a look at the different types of infections.

TROJAN HORSE – Named after the mythological wooden horse used to sneak Odysseus and other Gree heroes into Troy, a Torjan horse will masquerade as a legitimate program but will unleash a harmful payload once installed.

WORM – Computer worms are self-replicating programs that burrow into systems, seeking out vulnerabilities to exploit.  The ability to spread without any user action makes them particularly dangerous.

SPYWARE – Ever fell like you’re being watched?  If your PC is infected with spyware, you just might be.  Even worse, spyware not only monitors your activities but can also hijack your system with redirected web searches and other annoyances.

POLYMORPHIC – To avoid detection, polymorphic malware constantly changes its own code, often using encryption with a variable key.  This stealthy technique poses a problem for typical scanners.