According to Microsoft.com, a computer virus is a software program that reproduces itself in order to interfere with computer operation. Viruses may cause data corruption or may lead to deletion of important files stored on your hard drive. They are usually spread as email attachments, downloads, or as links or attachments with instant messages. If you suspect that you may have inadvertently downloaded or opened a virus, there are several free anti-virus removal tools available from reputable sites.

F-Secure Easy Clean

F-Secure Easy Clean is a free program to remove viruses, worms, and other malware. The tool scans for infections and removes any it finds. It displays the results and the action that was performed. If a rootkit is found, F-Secure requires you to reboot your computer and the virus is removed after your system reloads. The minimum system requirements include Windows XP SP2 or SP3, Windows Vista, and 256 MB of RAM. It can execute with or without an active internet connection and can be easily transferred to other computers as a downloadable, executable file. It is recommended that files are backed up prior to use in the event a file may become corrupted and removed. Additionally, you must turn off your antivirus program to allow the F--Secure Easy Clean to access all the files; including those which may be blocked by your antivirus program to ensure a clean system. Although the program does effectively remove viruses, users must still have a valid antivirus program running in order to protect from future infection.

Microsoft Security Essentials

Microsoft offers a free program called Microsoft Security Essentials that provides real-time protection against viruses, Trojans, worms, spyware, and other malicious software. It does require that you are running a genuine copy of Windows and it is compatible with Windows Vista, Windows 7, and Windows XP SP2 and higher. After your version of Windows is validated by the online Microsoft Genuine Advantage software, it will update automatically. It runs in the background and scans at specified times. It alerts you when a problem has been detected.

Spyware Doctor with Antivirus

PCTools has an award-winning free spyware and antivirus program called Spware Doctor with Antivirus. The program is compatible on the Mac and Windows operating systems and provides protection and removal of thousands of adware, spyware, keyloggers, Trojans, viruses, and other forms of malicious software. Spyware Doctor is recognized as an industry leader in virus and malware detection and removal programs. It has been reviewed and test by PC Magazine, CNet, PC Pro Magazine, and other reputable technology research entities. The program requires Microsoft Windows XP SP2 + , Vista, or Windows 7.

Source:

Microsoft -Computer Virus Information

More Information:

F-Secure Easy Clean

Microsoft Security Essentials

PC Tools Spyware Doctor with Antivirus