While no current antivirus on the market free or otherwise commercial will guarantee 100% protection, despite of their claims, I have researched and tested, as part of my job, and do recommend to my customers either ESET NOD32 or Kaspersky Internet Security 2010.Additionally, it has been my experience that AVG, along with some other free antivirus software, it is not as accurate as the ads may lead you to believe, and in fact, it has missed nearly 45-50% of the virus, worms, et al, malware on the Internet. Hence, I would not recommend it.
I would recommend you to continue to run, periodically as you state, the Malwarebytes, which is a great application, and SuperAntiSpyware, as both of these freely available software do have great reviews, but do invest in Kaspersky 2010 or ESET NOD32. The subscription is not expensive, but the headaches they will save you in the long run are absolutely worth it. Make sure you have a stateful packet inspection firewall either at home, as an external device incorporated in your cable-modem or in addition to that, or software based, like the one that comes with Kaspersky. The current Windows XP firewall that comes with SP2 is not that good in comparison. In fact, it is really not accepted as a good firewall by serious IT professionals. I am an engineer.
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