I am loosely associated with a large organization which has thousands of PCs. The organization takes the virus threat very seriously. They have standardized on Norton/Symantec. I've bought it and use it at home and it automatically updates very frequently. I must average 2 e-mails w/ virus each day. It catches them all.
While I am using free Zone Alarm firewall, I don't know if it the "best", but it's highly spoken of.
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You'll probably also want free POPUp Stopper, Which is very effective at killing popup ads.
I find POPFile to be VERY helpful. It classifies your incoming e-mail and can put the spam into a special folder/directory of your choice. Free, but I have donated. After the first couple of weeks of training, it takes 5 minutes of maintenence a couple of times a week to keep the criteria up to date. With that care, it has a misclassification error rate of 1% or 2%.
MailWasher can be used to manually inspect the Subject, From, and To fields of your email and size BEFORE downloading. This way you can delete the large virus-ladden fake messages before downloading. I don't think I'd bother with it if I had high-speed network access. A good AntiVirus program will kill those messages after download.
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Your ISP may also do the popup stopping, and try to do the spam mail classification
Welcome to the PC world of virus targets.
SC