A computer virus is malware attached to another programme - such as a document - designed to replicate itself and spread
Once executed, the virus infects files in order to make copies of itself, generally without being detected by the user. Many viruses are harmful and can destroy data, slow down system resources, and log keystrokes.
Prevention is better than cure! Computer viruses are contagious but the best doctor for your PC and other devices is you. And make sure your anti-virus software is up to date.