Ways to prevent computer viruses: Anti-virus software and other preventive measures: Anti-virus software detects viruses in two common ways. The first and most common method is to identify a virus from a list of virus signatures. The main problem with this detection method is that users are protected only from the viruses mentioned in the aforementioned virus definition updates. The second method is the heuristic algorithm which is detected by the general definition of the virus. This method can detect viruses without being identified by the anti-virus signature firm. Repair process: Once a computer is infected with a virus, it is dangerous to use it without having to reinstall the operating system. However, there are several ways to repair a virus-infected computer. These methods depend on the type of virus and the degree of infection. Virus Removal: The process of undoing a damaged system on Windows XP is known as System Restore , which restores the registry and important system files to their normal state. Many times its application causes the virus to hang on the system and subsequent hard reboot will take it to the previous state of damage. However, some viruses disable the restoration system and other important tools such as task manager and command prompt. One of the viruses that do this is called Sydor. Administrators have the ability to disable these tools for other purposes. The virus does the same thing by modifying the registry , so that when an administrator runs the computer, other users, including himself, are prevented from using these tools. When an infected tool becomes unusable through a virus, it is called " Task Manager has been disabled by your administrator." Gives the message. Reinstalling the operating system: If a computer has a virus that cannot be removed by anti-virus software, reinstalling the operating system may be necessary. To do this, you need to delete the hard drive completely (you need to delete the partition and format it).