A computer virus is a computer program designed and written to make additional copies of itself and spread from location to location typically without one’s knowledge or permission. Viruses add their code to your computer when an infected file or program is executed on your computer. Some viruses display symptoms such as unique error messages, and some cause damage to files on an infected computer. A program does not have to perform outright damage (such as deleting or corrupting files) in order to be called a “virus”.
The most common categories of viruses are:
- Boot viruses that become active and run when the computer is restarted, or when restarted with an infected external storage device in the drive
- File viruses which attach themselves to executable program files and activate when the program is run
- Macros viruses which attach themselves to documents and templates so that when the file is opened the virus becomes active.