Great place to wake things up. Ran across this on my list of headlines:

Source: Security Ticker

F-Secure has reported about the first known rogue antispyware program for MacIntosh computers. Macsweeper is what it goes by. With the growing number of reported fake codec zlob trojans made for Macs, this doesn't surprise me. The first known Mac fake codec was reported just last November. Since then, there has been a steady release of Mac fake codecs to go along with the Windows versions. The last one discovered was on January 11th. If you go through Sunbelt's blog, you'll find many more.

For now, I'm not sure how you remove it, but it appears to be mainly a nuisance. More updates on this later.
MacSweeper did respond as noted here by F-Secure. I think this is just showing that regardless of platform you can face issues and get caught with your proverbial pants down.