Worms generally use networks to spread. This has a disruptive effect on the networks and host computers as this reproductive process uses up more and more computing space in memory as well as wasting valuable processing time. The Trojan Horse The Trojan Horse masquerades as a legitimate program that appears to be useful, while hiding malicious code. When a person attempts to open and use the program, the virus is activated. The Code Bomb contains dormant malicious code that is later triggered by specific circumstances.
Typical triggers are specific dates or a certain number of system starts.
The term polymorphic is used to describe computer viruses that mutate to escape initial detection by traditional anti-virus software.