LYCOS RETRIEVER 
Viruses (Malicious Software): Programs
built 262 days ago
Viruses (Malicious Software) also shows up in the Retriever categories:
Viruses (Living Thing) , and more.
Viruses (Living Thing) , and more.
Fred Cohen has proven mathematically that perfect detection of unknown viruses is impossible: no program can look at other programs and say either "a virus is present" or "no virus is present", and always be correct. But, in the real world, most new viruses are sufficiently like old viruses that the same sort of scanning that finds known viruses ... finds the new ones. And there are a large number of heuristic tricks that anti-virus programs use to detect new viruses, based either on how they look, or what they do. These heuristics are only sometimes successful, but since brand-new viruses are comparatively rare, they are sufficient to the purpose.
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Today, security threats fall into five basic categories: viruses, trojan horses, adware/spyware, hijacking, and system penetration/data theft. There is increasing overlap among them. An adware program, for example, may arrive as a trojan horse, function as adware, and have a backdoor component that permits data theft.
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Trojan Horses are closely related to computer viruses, but they differ in that they do not attempt to replicate themselves. More specifically, a Trojan Horse performs some undesired -- yet intended -- action while, or in addition to, pretending to do something else. A common example is a fake login program, which collects account information and passwords by asking for this info just like a normal login program does.
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