Simple Computer question re: viruses, trojan horses and worms

[NaMeaHou]

Can someone give me a simple definition of the difference between these? I can't seem to grasp the difference between a trojan horse and worm in particular.

Thanks for your response

[Don_G]

1. Basically

A Trojan Horse is a program usuaully sent by an e-mail attachment that opens ports on your computer so it's vunerable to attack.

A worm is basically the same, only it exploits weaknesses in an operating system (like XP) to open one or two specific ports.

[NaMeaHou]

3. Thank you -

that helps. So, a trojan horse will probably be let in through an email attachment. How is it different from a regular old everyday virus?

[Don_G]

5. A Virus

Is a program that will basically trash your computer.

A hacker scripts a trojan or a worm so he can use your computer for his purposes like a denial of service attack.

[TrogL]

2. a trojan horse

gets into your computer disguised as something else. And does damage. It doesn't necessarily replicate.

A worm is self replicating. Theoretically a trojan can be a worm.

[Kellanved]

4. there is no [longer a] difference

In state-of-the-art Software Engineering publications all of those are "trojan horses".
One might construct a (historic) difference: a "worm" uses a security issue to invade and replicate itself; a "trojan horse" is introduced into the system disguised as something else, a programm doing more than it should do (for example offering access to outsiders).
However many worms are/include trojan horses and vice-versa - so a "trojan horse" is a program doing something not specified. Many many applications fall under this definition.

[GregW]

6. Explanation from Symantec's knowledgebase

http://service1.symantec.com/SUPPORT/ent-security.nsf/pfdocs/1999041209131148?Open&dtype=corp