The Bests Virus Protection

The most important computing advice is "back up your files", which helps to safeguard your data if you ever get a virus. The second most important principle is "run an anti-virus protection program". If your anti-virus program does not include a good firewall, you must obtain one of those as well.
Modern computer viruses are more virulent than ever. It is critically essential for the protection of all of the valuable programs and information on your computer that you run a good anti-virus protection program. Most of these applications can regularly update their database over the Internet as the threats evolve and automatically keep your anti-virus protection up-to-date and your computer safe.
FOSS. The following sites provide free open source software options:

• ClamAV
• OpenAntiVirus

Indexes. The following indexes list companies that provide anti-virus protection programs and services:

• Google - Anti-Virus
• Freebyte's Guide to free Anti-Virus Software
• Yahoo - Virus Protection

Commercial. The following anti-virus protection providers have been around for several years - check recent reviews:

• Avira.com
• BitDefender.com
• CentralCommand.com
• F-Prot Antivirus
• F-Secure Anti-Virus
• Kapersky Labs
• McAfee Associates' VirusScan
• NOD32 Ireland
• Panda Security
• Sophos Anti-Virus
• Symantec's Norton Anti-Virus
• TrendMicro.com

Historical:

• Dr. Solomon's Anti-Virus Toolkit (DRSolomon.com)

Maintenance. Once you have installed anti-virus protection, take the following additional protective measures:

• Never use a floppy disk, CD, DVD, tape, or other external media that has been on someone else's computer without first scanning it with your anti-virus protection program, which should be set to scan all media by default. If you lend media to someone else to copy a file, write-protect it first so that it won't get inadvertently infected.

• Protect your perimeter. Make sure your anti-virus protection settings are turned on by default to scan files incoming over email and downloaded off the Internet.

Infection. Computers that run good anti-virus protection usually don't get infected. However, if you are sure that your system has somehow got a virus anyway, you can take the following steps:

• Immediately shutdown your computer, and do not reboot it from the infected disk, in order to prevent the virus from wreaking more damage.

• Boot the computer from some clean external media such as a bootable floppy, CD, DVD, or external disk that has previously been scanned by your anti-virus protection.

• Run your anti-virus protection software from the clean boot disk, on the infected disk, and if required fix or delete infected files and replace them on the infected disk.

• If you need help or your anti-virus protection can't clean the disk, then you are best advised to take your computer to a good professional repair shop where they have tools to try and clean and recover your disk as best as possible.

Keep in mind that anti-virus protection sometimes generates false alarms -- a common cause is when a program file has changed size but for a valid reason. Another common indicator that you may have a false alarm is if your anti-virus protection claims that a file may contains a virus but doesn't know the virus's name. Don't delete files unless the anti-virus protection software specifically recommends it, recognizes the viruses name, and it otherwise looks like a reasonable suggestion.