All "I thought Macs couldn't get viruses/spyware/malware/adware/etc!! LOL!" jokes aside... I'm not entirely sure about any malware scanners and removers for Macs. I don't think Malwarebytes, which I think a lot of people recommend for PCs, works with Macs. I didn't see it in their specifications.
Anyway, if you go to CNET, and type 'malware removal', you can search by Operating System and cost. There are a few free scanners and removers, but they don't have seem any reviews from either the editors or users. As such, I can't be entirely sure of their effectiveness/safety.
Here is one I found simply by looking at a couple websites on the topic of "Malware on Macs" via Google. (GOOGLE. USE IT!!)
ClamXav
(Please note: I have done just a quick and dirty search. I'd recommend researching the topic by yourself via forums for Mac users before you download programs off the web)
A lot of malware/spyware/adware/what-have-you scanners and removers really only do a good job if you pay for them. There are good, free, reliable alternatives for PCs, but not sure about Macs.
And I'm not entirely sure about whether pay-for AV programs would find what we call malware or spyware. I know that sometimes Symantec won't find or identify threats that Adaware or Malwarebytes identifies (I have Symantec Endpoint or whatever the newest one is. Free through the university if you're a student, staff or faculty)
On a side note, for those Mac users that use Virtual PC, you can still get PC viruses even though you're running a Mac. Plus, files sent by PC using friends, family and colleagues could perhaps find a way to mess with your computer.