Document viruses

Document or “macro” viruses take advantage of macros – commands that are embedded in fi les and run automatically.

Many applications, such as word processing and spreadsheet programs, use macros. A macro virus is a macro program that can copy itself and spread from one fi le to another. If you open a fi le that contains a macro virus, the virus copies itself into the application’s startup fi les. The computer is now infected.

When you next open a fi le using the same application, the virus infects that fi le. If your computer is on a network, the infection can spread rapidly: when you send an infected fi le to someone else, they can become infected too. A malicious macro can also make changes to your documents or settings.

Macro viruses infect fi les used in most offi ces and some can infect several fi le types, such as Word and Excel fi les. They can also spread to any platform on which their host application runs.

Macro viruses fi rst appeared in the mid-1990s and rapidly became the most serious virus threat of that time. Few viruses of this type are seen now.