Viruses are written by malicious programmers who wish to cause problems for other computer users.

The primary source of infection these days are emailattachments followed by illegal software and infected files from the internet. If you have up to date anti-virus software installed this will immediately warn you of any infection. If not, there is usually no evidence of the virus and the user is not usually aware of it until something goes wrong.

Devices without antivirus software infected with viruses