Worm
Worm
In a computer, a worm is a self-replicating virus that does not alter files but resides in active memory and duplicates itself. Worms use parts of an operating system that are automatic and usually invisible to the user. It is common for worms to be noticed only when their uncontrolled replication consumes system resources, slowing or halting other tasks.
You can find more information about worm in this website
http://searchsecurity.techtarget.com/sDefinition/0,,sid14_gci213386,00.html
