Most people never experience a computer virus, but it pays to be cautious with valuable data such as an inventory, account books, or customer mailing list. Most viruses are attached to programs, not word processor or database files. If you download a lot of free software from the Web, infection is possible as soon as the downloaded program is run. Even purchased software is dangerous if it is an illegal copy. Recent viruses have caused serious problems in the Middle East and Southeast Asia, where pirated software is more common.
Macros are crude, user-written programs that are stored within a word processor or spreadsheet file.
They are used for things like automatically generating a mailing label from the heading of a letter or running a statistical analysis of spreadsheet data. In the hands of vandals, macros can damage files or flood the Internet with spurious messages. There are two reasons. First, these programs are by far the best sellers in their respective fields, so their users are a big target. Second, Word and Excel macros can invoke a far more powerful general-purpose programming language that can reach into all corners of the computer.