What's the difference between a worm and a virus

What is the technical difference between a worm and a virus?

As I understand it, a worm actively seeks out new victims (or attempts to send itself to new victims) once it has infected a host. A virus won’t do this, if my understanding is correct.

Actually, a virus replicates itself by inserting itself into other programs, so that when that program is opened the infection spreads.

A worm, on the other hand, is a self-contained program. Once executed, it replicates by sending out copies of itself, but it does not insert itself into other code.


McAfee Virus Glossary

Symantec’s description of the difference between a worm, virus and trojan.