Is Sophos a legitimate antivirus?

http://www.sophos.com/en-us/products/free-tools/sophos-antivirus-for-mac-home-ed ition.aspx

I downloaded it a while back, just for some extra protection on my MacBook Pro, which is running OS X. Even though I've heard that viruses or any other malware doesn't exist on OS X, I still downloaded it for extra protection.

Is this a legitimate antivirus? I've been recently warned that there is a Mac-virus out there (actually, I've heard from several people that there are some Mac-viruses, but they're uncommon), so is Sophos actually legitimate or just another antivirus scam...?