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[ The PC Guide | System Care Guide | Data Loss and Virus Prevention | Virus Detection and Protection | Virus Scanning and Antivirus Software ]

Viruses in Memory, and the Importance of the Clean Boot Floppy

In order for a virus scanner to have any chance at reliably detecting virus infections on a hard disk or floppy disk, it must be allowed to operate in a clean environment. The first thing that a virus scanner will normally do is to examine the system memory when it is run, looking for any viruses that may be memory-resident that could impede virus detection. Most scanners will not run if they find a virus in memory. A file-infector virus could be in memory if an infected program was run before the virus scanner; a boot sector virus will normally infect memory as soon as the PC is booted.

The best way to scan for viruses is to start the system with a clean virus-checking boot floppy before running the scanner. This ensures that if there is a hard disk boot sector virus, it is not given a chance to load into memory before you scan. In order to boot from a clean boot floppy in this manner, your system must be set to try to boot from the floppy first in its boot sequence. (If it isn't set to boot from the floppy first then you can't use a clean boot floppy in this manner, but you also have much less chance of getting a boot sector virus.)

A clean virus-checking boot floppy should be created as a bootable floppy with whatever operating system you are using. It should ideally have the virus scanning software on it, and should be write-protected to eliminate any chance of it getting infected itself. Even if the virus software is not on the disk, booting from it instead of the hard drive will bypass viruses located in the hard disk boot sector or startup files. This boot disk should be one of the boot floppy disks that you keep as part of the backups of your system.

Next: Types of Scanners and Other Antivirus Software Protection

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