The main targets of a virus are program files (files with an EXE or COM extension), which can be run to perform specific operations. Increasingly, other types of files and documents can also be infected such as web pages (HTML), Word documents (DOC), Excel spreadsheets (XLS), etc.

If a file becomes infected, it may behave in a completely different way than before. The consequences of an infection to the system can therefore vary enormously.

As files are often stored on disks or drives (hard drive, CD-ROM, DVD, diskettes, etc.), the damage caused by the virus may also affect these elements.

For more information, go to Transmission and camouflage techniques.