ClamXav is a popular virus checker for OS X.
I have been working on ClamXav for more than 10 years now, and over those years, I have invested a huge amount of my own time and energy into bringing ClamXav to where it is today -- one of the most trusted and recommended anti-virus solutions for the Mac. In the past, other priorities got in the way and I wasn't able to focus on development as much as I would have liked, but that stops now. ClamXav is now a commercial product. It's being sold through a new company (Canimaan Software Ltd) but don't let that fool you -- I'm still the owner and lead developer.