Virus

Malware exists in several types, each of which has its own propagation methods and targets:

1. Definition: A virus is a malicious software that attaches itself to executable files. Viruses replicate (= create copies of themselves) and thereby spread among the files of a device and possibly over the network to which the device is connected.
   
   This is the most known type of malware and is sometimes used, in layman terms, as a synonym for malware.
   For instance, we tend to say 'anti-virus' and not 'anti-malware'.
   
   Reason for the name: Due to the similarity to a biological virus that attaches itself to a living thing's cells and starts replicating.
   Propagation: Infects and modifies a computer system's files when an executable carrying the virus runs (in many cases, with the help of an unawared user who executes the program.)
   Examples of well-known viruses: Michelangelo, Brain, Klez, SQL Slammer, and Blaster.