I am using a program called stop-sign click here , which I have had for about 2 years with no trouble. This costs about $40 (£23) per year, but for that you get anti-virus, Firewall, Threat scanner and a few other goodies thrown in.
Some programs see it as spyware, because it loads itself deep into the system to catch nasties before they can activate.
If you do get an infection that is not covered by their anti-virus software, they will write a custom fix especially for your machine at no cost.
I initially run it along side Norton Anti-virus, but Stop-sign always beat norton to the punch.