Even for an expert, removing a virus properly from a system is often a daunting task without the help of specific tools designed for the job. Some viruses and other unwanted software (including spyware) are even designed to reinstall themselves after they have been detected and removed! Fortunately, through updating your computer and using free, trial-period, or low-cost antivirus tools offered by many companies, you can help permanently remove (and prevent) unwanted software.

If you already have antivirus software installed on your system, it's very important to keep it current on a regular basis with the latest updates (usually called definition files) that help the tool identify and remove the latest threats. In addition, not all antivirus tools are created equal; if you find that the one you use isn't working to your satisfaction, you should do some research and try an alternative.

Basic viruses typically require unwary computer users to inadvertently share or send them. Some viruses that are more sophisticated, such as worms, can replicate and send themselves automatically to other computers by controlling other software programs, such as an e-mail sharing application. Certain viruses, called Trojans (named after the fabled Trojan horse), can falsely appear as a beneficial program to coax users into downloading them. Some Trojans can even provide expected results while quietly damaging your system or other networked computers at the same time.

(above wrıtıng www.microsoft.com from receipt)