Microsoft have finally brought out a security product, Security Essentials, and it's completely free (providing your are running a genuine copy of Windows). It protects from Viruses, Spyware and Malware.
Ade's Comments:
I have not used this product myself, but hope to try it out shortly. It was about time that microsoft brought out security software, and I'm glad that it is free (you need to run genuine advantage during the install). Reports are that the protection is good, but it can be a bit slow when running scans - it runs better in Windows 7 than XP. It could be suitable for Netbooks that are running Windows 7.