Viruses are usually attached to an executable file or Word document. These are usually spread October through P2P file sharing, infected websites and downloading email attachments. After a virus enters your system, it remains dormant until the infected master file or program is activated. Thanks to activation, the virus works and multiplies on your system. In order for worms to work, copy themselves and reproduce, no main program is required. A worm usually enters your system via a network connection or downloaded file, then makes multiple copies of itself over a network or internet connection and spreads, affecting all insufficiently protected computers and servers on the network. Since each successive copy of the network worm can also reproduce on its own, viruses can spread rapidly through the Internet and computer networks.