This question comes up all the time. The problem is that it’s both trivial to answer and it’s impossible to answer. There’s a strong argument that says there’s no objective answer at all.
It’s all about opinion, so let me tell you mine: there is no best anti-virus tool. There are several good ones, but none are perfect. And in fact, one that works well for your friend may not work at all for you.
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In search of perfection
There are several problems at play here that make this an almost impossible question to answer.
For one thing, as I said, there is no perfect anti-virus tool. There just isn’t. There is no tool that will catch absolutely every virus. The best you can hope for is one that will catch most – and even “most” is kind of up for debate.
Second, different anti-virus tools are written in different ways and actually impact different systems differently. One, for example, might use a lot of memory. If you have a lot of RAM, it might be an awesome anti-virus tool. If you don’t have a lot of RAM, perhaps it will slow your system to a crawl.
And of course, what it means to have a lot RAM will vary from computer to computer, since different machines will have different amounts of software installed on them. It will also vary from anti-virus tool to anti-virus tool.
And of course the issue may not be RAM. Perhaps there’s some other aspect of your system that different tools exercise differently: for instance the disk, the CPU or perhaps even the network connection. As a result, different people with different machines will have different experiences even with the exact same anti-virus tool.
And it actually gets even weirder.
What is a virus, anyway?
There’s no agreement on what is and is not a virus. Sure, the big, hairy obvious ones are … well, obvious. But how about Foistware? Spyware? Toolbars? Some of these things you perhaps even asked for, whether you were aware of it or not.
Different anti-virus programs will make different choices; choices that some people think are better than others, and other people think are absolute nonsense. Choices that make labeling one program “the best” almost impossible.
So, knowing that there is no best anti-virus, what’s a user to do?
Anti-virus tools are only part of the solution
The single most important thing you can do is just realize that your anti-virus tool cannot protect you from everything; even if it were this so-called mythical “best”.
Anti-virus tools are, and have always been, a part of a much larger picture. That picture includes a good anti-virus tool; a good anti-spyware tool; a firewall; keeping your software (all of it) as up to date as possible; securing your router and other hardware, and above all, behaving safely. There is no security tool that will save you from actions that you are determined to take.
And lastly, I will refer you to my article, “What security software do you recommend?” for some specific programs to consider.