You don't need it. There is seriously no way your friends could have gotten them. There are zero viruses in the wild that do destruction. The proof of concept ones that do exist require you to type in your username and password. I've been using my mac for over three years without a single problem. My dad and my sister have similarly had no problems. I know quite a few Mac people all with no virus problems.
In the case you still feel like you need protection (which'll just steal power from your computer), you can use ClamXav
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If I'm gonna jump off the cliff, and you're gonna get pushed off the cliff,
why don't we hold hands on the way down?