Viruses are computer programs that can spread by making copies of themselves.

Computer viruses spread from one computer to another, and from one network to another, by making copies of themselves, usually without your knowledge. Viruses can have harmful effects, ranging from displaying irritating messages to stealing data or giving other users control over your computer.

A virus program has to be run before it can infect your computer. Viruses have ways of making sure that this happens. They can attach themselves to other programs or hide in code that is run automatically when you open certain types of fi le. Sometimes they can exploit security flaws in your computer’s operating system to run and spread themselves automatically.

You might receive an infected file in a variety of ways, including via an email attachment, in a download from the internet, or on a disk. As soon as the file is launched, the virus code runs. Then the virus can copy itself to other files or disks and make changes on your computer.