Avast 5 free is a good antivirus and Malwarebytes is top-notch anti-spyware application. Still you can improve your security by adding some extra protection.
Additional on-demand scanner:
Hitman Pro (Trial) -
link
An on-demand scanner using multiple anti-malware engines and cloud technology. It offers unlimited free scanning but once you use it to remove detected malware it switches to a 30-day trial version. I recommend using it after you've scanned your hard-drive with the other products you have installed.
Additional browser protection:
WOT -
link
To help you avoid malicious sites you can use Web of Trust (WOT) a website rating browser plugin. After you add it to your browser make sure you only visit websites rated "Green" by WOT.
Secure DNS providers
Such as: OpenDNS, Norton DNS, Comodo DNS, etc. They work as your
normal DNS servers but they also filter-out unwanted sites (sites serving malware, pornographic material, etc.)
Other considerations:
Keep both Windows and installed software up-to-date
Some malware gets into your PC by exploiting vulnerabilities present in Windows and in software applications you are using. Updates fix those vulnerabilities and improve your security. To keep your applications up to date you can use
software update monitors (File-Hippo update checker, Secunia PSI)
Disable autorun on Windows XP -
link
Some malware gets into your PC through infected USB thumb-drives as soon as you insert that drive. Disabling autorun prevents this from happening.
Sandboxie -
link
Probably the most secure way to protect your browser. Sandboxie runs your programs in an isolated space which prevents them from making permanent changes to other programs and data in your computer. You can use Sanboxie for free for as long as you like, but after a period of 30 days it will display a nag-screen.
