A virus is a program that runs on your computer, usually without your knowledge, that performs malicious tasks such as removing files, disrupting the smooth operation of your computer, or sending personal information to unknown parties. Network-aware viruses that spread through the Internet are referred to as Worms. When your computer is infected with a virus, you may notice a dramatic reduction in responsiveness when opening programs, or problems staying connected to the internet.  These symptoms are not necessarily evidence of a virus, but if the change is abrupt and recent, it is worth scanning your system with a virus removal tool.