Note that these programs often can't undo the damage to your files after a virus has wreaked its havoc, so the time to take action is now, before you have to deal with a virus in your system. For maximum protection, you should scan for viruses at start-up or whenever your run a program or download something from the Internet. Check below to see how to set up your options in a typical antivirus scanning program.

From Windows 95/98, Select Start/Settings/Control Panel. From the Control Panel window, open Add/Remove Programs. Select the Startup Disk tab and follow the instructions. Have a blank floppy disk handy.

Macs come with a bootable CD-ROM, so a floppy start-up disk isn't necessary. To boot from a CD-ROM, insert the disc into the CD-ROM drive and press c as your Mac starts up.

Some files can create false alarms; an exclusion list lets you skip them. Configure your antivirus software to check vital system files and memory during the boot process. For maximum protection, scan files whenever they are created or used. When the software locates a virus, you'll want to be able to repair or delete the infected file.