Symptoms of an infection vary depending on the type of virus you have, but there are some general guidelines. A common symptom of a boot sector infector is problems with booting: the system doesn't boot or displays odd messages when booting. Your software may note a change in the boot sector or memory map.

Symptoms of file infectors can be executables that used to work but are now failing to load correctly. Your antiviral package may indicate that something "goes resident" in memory and stays there after running an application.

A macro virus infection is usually not as subtle as file infectors or boot sector infectors. With a macro virus all your documents may only offer you the option to save them as templates. You may notice "extra" macros that did not come with your word processing package and that you did not create.

As soon as you note a symptom, investigate! You may not have a virus, or even a serious problem, but don't take chances.