Malicious Mobile Code

Protecting Yourself from Viruses

After every virus cleanup comes the process of preventing it from happening again in the first place. For DOS viruses, try the following steps.

1. Disable booting from the floppy diskette drive.

Go into your ROM BIOS and disable booting from drive A. It’s the easiest, single biggest thing you can do to decrease your risk of boot virus infection. If your PC can’t boot from the floppy drive, it can’t get an infection from a pure boot virus. And since most boot viruses don’t come in from dropper or multipartite infectors, you’ve just about eliminated the threat. When I first tell people to do this step, they almost always ask what should they do if they need to boot from the floppy drive in the future (e.g., to scan for a computer virus)? Easy. Just reenable it. It takes 15 seconds.

2. Use ROM BIOS to write-protect the hard drive’s boot areas.

Today, most ROM BIOS chips allow you to write-protect your hard drive’s boot areas. I’ve seen it called “Virus Protection” or “Boot Sector Write Protection.” It’s an easy feature to turn on and off. Typically, you don’t need to modify a PC’s boot records unless you are repartitioning the hard drive or upgrading the operating system. I have seen a few cases where legitimate programs (e.g., Norton Disk Doctor) needed to write to the MBR or operating boot sector and were prevented by the ROM BIOS. It’s a little disconcerting to see a “Possible Virus Attempting to Modify Your Hard Drive’s Boot Sector” error message ...