What are viruses?

Some articles on viruses:

Computer Virus - Vulnerability and Countermeasures - Recovery Strategies and Methods
... One may also minimize the damage done by viruses by making regular backups of data (and the operating systems) on different media, that are either ... and anti-virus products will identify known viruses precisely before trying to "dis-infect" a computer otherwise such action could itself cause a lot ... New viruses that anti-virus researchers have not yet encountered (zero-day viruses) therefore present an ongoing problem, which requires anti-virus packages to be updated frequently ...
List Of Computer Viruses (all) - List of Viruses and Related Programs - Related Lists - Similar Software
... Adware Malware Spam viruses Spyware Computer Worms viruses Trojan viruses. ...
List Of Computer Viruses (all) - Scope
... major variants the list of "in-the-wild" viruses, which list viruses in active circulation, and lists of all known viruses, which also contain viruses believed not be in active circulation (al ... in-the-wild lists contain a hundred viruses but full lists contain tens of q ...