They use self-replicating viruses and spyware. It costs them nothing so they don’t care how many people are affected or what the damage is.

You need a multi-layered defence to keep them out:

• Security software: anti-virus, anti-spyware and a firewall or security suite that includes all three. This is like keeping your doors and windows locked at home.
• Keeping your computer up to date, blocking spam emails and using an up to date web browser will make it harder for them to get into your PC in the first place.
• Making a regular backup of your music, pictures and other files is also a good idea, but it’s a last resort like insurance.
• It’s also a good idea not to use your computer in administrator mode. It’s better to make a user account and log in with that for day-to-day use. In Microsoft Windows Vista, keep User Account Control switched on.
• Lastly, protect yourself against eavesdroppers and freeloaders by using encryption on your wireless network.