virus protection on macbook air?

You don't need to. If you want to, use ClamXav.

(70127)

If you run Microsoft Windows on your MacBook Air, yes, you'll want malware protection.

OS X works nicely out of the box.

But it's possible to install stuff that can or will cause problems.

There's very little malware stuff that'll hit you unexpectedly; what's been around lately has targeted Oracle Java or Adobe Flash vulnerabilities, or it's malware that's managed to convinced the user to install it on behalf of the attacker - examples of the "install me" stuff include various (free) "anti-virus" tools, "video players", "Flash Player updates" (those not from Adobe) or other "software updates", or (unnecessary) "performance optimizers" or "cache cleaners", etc.

On OS X, learn to install from the main distro sites only (eg: if you use Flash, only install it by going to Adobe's web site), learn to ignore the Facebook malware warnings ad campaigns, ignore the rest of the advertising pop-ups that are around the net and the rest of the OMG YOU'RE INFECTED!!!! stuff, don't install something that you didn't expressly go looking for, either don't install Oracle Java (and it's not installed by default on 10.8) or keep Java disabled until and unless you're actually using it (and that's Java, which is very different from Javascript), and either don't install the Adobe Flash Player tool or remove it and if you have it installed keep it current and yourself get a Flash blocker for Safari or whichever browser you're using.

And the usual advice: keep your OS X and add-on tools current.

And never click on banners or links outside Apple's page if they message to improve performace or modify computer features (Like "Slow Mac?"). Refer to Apple page or AppleCare support.