3. How do they spread?

The most common way of getting computer viruses these days are:

• email attachments
• infected web pages
• downloading a file from a web page

Another way is to load an infected file into your computer from some kind of storage device:

• memory stick
• CD/DVD

Note: The CD and DVD products from reputable companies are extremely unlikely to contain a virus. It is the personal 'burned' ones that are a potential problem.

It is also possible to pick up a computer virus through what is known as 'peer to peer' file sharing networks. These are internet networks that are used by people to share files amongst each other.

There is often no immediate evidence that your computer has been infected with a virus and you might be unaware of it for a while until it causes something to go wrong.

Basically a virus is spread by allowing it to run (technical term: "execute") on your computer, so any executable file or computer program can contain a virus.