Computer viruses are classified by the way they spread. Boot sector viruses are carried on floppy disks. They attach themselves onto the computer's boot sector, which is the part it uses when it starts up, and infect programmes as the computer runs them. When the programme is run, the virus is activated and attaches itself to other programmes on the computer.
Macro viruses are the newest type of viruses.
Macros are mini programmes built into word processing or spreadsheet applications, which combine a frequently-used series of instructions into a single command. A macro virus infects this global template file and then corrupts any file opened using it. The complex macros in Microsoft Word and Excel have so far been the main targets of these viruses. PC viruses do not affect Macintosh computers, but there are a few viruses targeted specifically at Macintoshes. Delve deeper Recent threats.