Computers are great tools, but they can also be mystifying. Sometimes a program will just stop working correctly for no apparent reason. It could just be a random glitch that can be solved by restarting the machine. But sometimes the solution is not so simple, especially if at the root of the problem lurks a computer virus.   A computer virus is a bit of programming code that gets passed from machine to machine by e-mail or the sharing of programs. Like a biological virus, on its own a computer virus can't do anything. But once it gets attached to something else, say a document or image attached to an e-mail message, it can wreak havoc.

Once you open the infected object, two things can happen. The virus will reproduce itself to infect other documents and may damage the overall functioning of your computer. Depending on the type of virus, it can simply clog up memory or, even worse, erase data. If your computer is connected to the internet, viruses called worms may infect your machine, then use its connection to seek out and infect other computers.

Unlike natural viruses, computer viruses are created by people and unleashed with the intent of doing mischief or harm. If you find that your computer has been infected, run a virus detection program to find the virus and destroy it. The best way to protect your computer is to install virus protection software that's always alert and looking out for harmful intruders. Plus, never download a program from iffy Websites or open unsolicited e-mail attachments. They may be harmless, but you never know when a virus might be attached and ready to pounce.