A Nematode is a basically a computer virus that attempts to remove another virus. For example, The Denzuko virus attempts to remove the "Brain" virus. The Netsky Windows Worm attempts to remove the MyDoom worm. Some Nematodes drop other viruses to the computer AND attempt to remove another virus. The Klez worm attempts to remove the CodeRed worm and others while dropping the Elkern virus. Most Nematodes remove registry values and registry keys that the virus they are trying to remove dropped. Some delete files, disinfect files, and more. Nematodes are like malicious antivirus programs.