Removing Viruses
The Threat of Viruses
Practically everyone today knows what a virus is. They are programs written with one purpose in mind--to destroy, modify or collect data or deny service to a particular computer or network. Viruses come in various types--viruses, Trojan horses, backdoor exploits, worms, and logic bombs, but they are all a threat to computing. Over 200 new viruses come out every month, and that number is rising. The importance of a good, updated virus scanner and a firewall cannot be overstated. I recommend a commercial antivirus program that will cost $20-$40, or a suite of protection programs, though a few decent free ones are available on the Internet. The purpose of this guide is to help you with the general idea of detecting and removing viruses, not with a particular program, but with any good scanner.
Detecting Viruses
Some viruses will have a visible effect on the computer, and others won't. If a drive suddenly disappears, disks become mysteriously corrupted, file are deleted, the computer boots erratically or slowly, or the computer is cycling constantly, then you may have a virus. Spyware can also create cycling disks and slow boots, so look for other symptoms. Viruses are more severe than spyware and harder to detect and remove. If you only have a cycling disk or slow boot time, and you're getting pop-ups, it's probably spyware. Run a spyware remover (See the Dealing With Spyware Guide for help).
Even if there are no visible symptoms, scanning your computer once a week is good computing practice. To scan your computer, usually all you have to do is right click or double click the tray icon and click the "Scan" button, or some have Explorer plug-ins that allow you to right click on a drive in My Computer and then click "Scan for viruses..." Either way, familiarize yourself with your particular virus scanning software and ensure it stays up to date. Here are some good settings to use in your virus scanner, wherever the options are:
Scan all files, not just program files.
Scan inside ZIP and archive files.
No exceptions, not even the Recycle Bin.
Scan all incoming mail, incoming downloads and floppy disk accesses.
Enable Auto-protect.
Scan in-memory threats.
Scan boot sectors.
Actions: always prompt.
These settings will ensure the most thorough scans possible, in general. If you have additional options, use them. No amount of protection is ever too much.
Once you've scanned for viruses, if nothing comes up--you're good and clean. Congratulate yourself and remember to scan next week.
Removing Viruses
Uh oh. Your computer has a virus. Your scanning software found it on a floppy or buried in \windows\system32. Now it's asking you what to do. The best thing to do is attempt to clean the file. This will usually work, and if it does, the virus scanner will roll on happily along to its next target. Occasionally, however, cleaning won't work. Now you have two options. You can delete it--which is the best idea if it's nonessential (you do make backups, right?), or you can quarantine it, though I don't recommend this unless you need the file for something, and even then it could spread to other files on your computer.
Sometimes, a virus is so nasty not even a deletion works. In this case, you're going to have to do it yourself. Write down the name of the file that is infected--path and all, and restart your computer into safe mode (F8 pressed before the Windows logo). When you get to safe mode, find the file and attempt to delete it manually, or run your virus scanner if it will run in safe mode. Once you have gotten rid of the file, kill it from the recycle bin, reboot and run your virus scanner again. If this doesn't work, you may want to try reinstalling Windows or taking it to someone who has better scanning software.
Alternately, you can make a boot disk from most virus scanners. Find this option under the virus scanner interface and prepare a fresh floppy disk for booting. Run the virus scanner's boot disk creator and reboot your system, following the instructions on how to scan and remove. If your virus scanner came on CD, put it in the CD drive and reboot your PC. Most virus scanning CDs have a boot-from-CD option, if your BIOS has the CD drive set for a higher priority than your hard drive. Some combination of these techniques will remove most viruses.
Keeping Viruses off Your System
Common sense rules here. Don't open emails from people you don't know or have no subject line, and don't open attachments, ever, unless the person who is sending it tells you about it in person, over the phone, in IM, or in a preceding email. Scan all downloads from the Internet, and don't download from shady sites. Stay off file-sharing networks, don't accept IMs from people you don't recognize, and scan your computer weekly. Keep your files up to date, Windows updated and back up your system. Disconnect from the Internet or shut your computer down when it's not in use. Keep a firewall up, even if it's just the Windows XP one. And stay away from warez!