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Chapter 2 – Introduction to Computer Viruses
Some viruses act very quickly, while others are set to go off at a certain time. Some
merely content themselves with spreading to other disks and volumes, but all
system viruses can potentially cause damage.
Trojan Horses
The name Trojan Horse comes from an episode in the war that opposed the Greeks
and the city of Troy, several millennia ago. The Greeks built a huge, hollow
wooden horse and gave it to the Trojans, apparently as a gift, before supposedly
sailing away and ending the war. While some of the Trojans were skeptical about
it, the horse was taken inside their stronghold. That night, Greek warriors emerged
from the horse, opened the city gates, and Greek soldiers from outside stormed the
city.
It is obvious that the Trojans were never told not to open attachments. The Trojan
horses that we are worried about are programs that look innocent and claim to do
a certain task, but actually contain malicious code or viruses. In many cases, Trojan
horses can be even more dangerous than other viruses. Some examples are
ChinaTalk, which looks like a system extension but deletes folders, or the famous
MacMag Trojan, which infected System files.
Worms
Worms are one of the oldest forms of viral programs on computers. They spread
by methods other than attaching themselves to files and applications, and can be
very difficult to find. One of the most serious worms on the Macintosh, called the
AutoStart worm, created invisible files that could destroy data and files.
Intego VirusBarrier X4 User's Manual
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