Viruses, worms, and Trojan horses are programs created by hackers that use the Internet to infect vulnerable computers. Viruses and worms can replicate themselves from computer to computer, while Trojan horses enter a computer by hiding inside an apparently legitimate program, such as a screen saver. Destructive viruses, worms, and Trojan horses can erase information from your hard disk or completely disable your computer. Others don't cause direct damage, but worsen your computer's performance and stability. Antivirus programs scan e-mail and other files on your computer for viruses, worms, and Trojan horses. If one is found, the antivirus program either quarantines (isolates) it or deletes it entirely before it damages your computer and files. Windows does not have a built-in antivirus program, but your computer manufacturer might have installed one. Check Security Center to find out if your computer has antivirus protection. If not, go to the Microsoft Antivirus Partners webpage to find an antivirus program. Because new viruses are identified every day, it's important to select an antivirus program with an automatic update capability. When the antivirus software is updated, it adds new viruses to its list of viruses to check for, helping to protect your computer from new attacks. If the list of viruses is out of date, your computer is vulnerable to new threats. Updates usually require an annual subscription fee. Keep the subscription current to receive regular updates. If you do not use antivirus software, you expose your computer to damage from malicious software. You also run the risk of spreading viruses to other computers.