A computer virus is a computer program that can copy itself and infect a computer without permission or knowledge of the user. Viruses spread by being attached to files or other programs. Viruses are frequently destructive; when the host program is opened, a virus can execute and cause your computer to crash, erase your hard drive, or do other damage.
If it is infected with a virus, your computer may run particularly slowly or exhibit other strange behavior, such as crashing or restarting on its own, or freezing or not responding to commands. You may receive error messages you have not seen before or see distorted dialog boxes or menus, or you may receive returned emails that you did not send. Symantec maintains a list of Virus Definitions & Security Updates that is updated daily; McAfee also maintains a list of current virus threats and definitions.
If you think your computer is infected with a virus, use your virus protection software to scan your computer and disinfect or delete any infected files.
Spyware and Malware
Spyware is software that secretly gathers information about a user while he/she navigates the Internet. Short for malicious software, malware is a program or file that is designed to specifically damage or disrupt a system. Malware and spyware can either be viruses (programs which piggyback on legitimate programs to spread and operate), or worms (which are programs that actively transmit themselves over a network to infect other computers).
Malware has to be written and tested by a human with malicious intent. It should not be confused with legitimate software that has bugs. People who are writing malicious code are often using it to profit by collecting credit card numbers, social security numbers, or other personal information.
Protect Your Computer
You should periodically scan your computer to detect any malicious programs (viruses or spyware) that may have been installed on your computer unbeknownst to you and are designed to collect sensitive information about you or to misdirect you to fraudulent websites. If your operating system offers free security software upgrades, you should install them as they become available.
Invest in virus protection software from a reputable source, and be sure to check for updates every few weeks. Avoid programs from unknown sources and stick to commercial software. Do not click on email attachments. Instead, download any files and use virus protection software to scan files or documents before you open the files.