Some viruses are simply nuisances and others actually destroy data.
This kind of virus attaches itself as a macro to a Microsoft Word or Excel file. This kind of program appears to be useful and harmless but can have harmful side effects such as destroying data or breaking security on the system on which it is run. A worm is a program that can make copies of itself, and spread through connected systems, using up resources in affected computers or causing other damage. Network Associates VirusScan is used in the library and throughout campus to prevent infection, detect and irradicate viruses. Copyright 2001 Northwestern University Library.