What is a virus, Trojan or worm?
A virus is a computer program that makes changes to your computer without your permission, getting it to do something you don't want. Often a virus spreads from file to file on your computer and it may then be passed to other people's computers.
Viruses can come in the form of Trojans or worms. These are malicious codes designed to disrupt your computer or let hackers steal information from your hard drive. They can also be used to take control of your computer remotely, bringing it into a botnet.
If you're lucky, a virus on your computer may only cause it to behave unusually rather than damage it. A virus can be very destructive by formatting your hard drive, overwriting your hard drive boot sector, or deleting files. A virus can even stop your computer working.
Computer viruses can spread quickly across the internet, causing a lot of damage in a short amount of time. It's inevitable that you'll pick up a virus when using the internet and emails, unless you have protection software.
If you think your computer has been affected by a virus, you can find out how to clear it here.