Avast can actually be a little bit high-resource on some systems (though not as bad as Norton). I use it myself on one PC and apart from that one issue it is every bit as good as my previous fave F-Secure. However, I have recently discovered NOD32 (which I use on a laptop, so resource-usage is a bigger issue). It is reckoned by the people who test such things to be the most effective available.
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