Free virus checker has the ability to detect both Windows and Mac threats. ClamXav can be setup up as passive or active: scan only the files you tell it to or your entire hard drive; you can also choo.
Clamxav 3
Back in the days before OS X, the number of viruses which attacked Macintosh users totalled somewhere between about 60 and 80. Today, the number of viruses actively attacking OS X users is...NONE! However, this doesn't mean we should get complacent about checking incoming email attachments or web downloads, for two reasons. Firstly, there's no guarantee that we Mac users will continue to enjoy the status quo, but more importantly, the majority of the computing world use machines running MS Windows, for which an enormous quantity of viruses exist, so we must be vigilant in checking the files we pass on to our friends and colleagues etc. For example, if you're a wise person and you've turned MS Office's macro support off then you're not going to notice that virus which is hiding inside this month's edition of Extreme Ironing.doc which your friend sent you. If you then forward that document to a less wise person who has not turned off the macro support, then you have most likely just sent him a shiny new Pandora's Box with a sign saying 'Open this end'!
Flippancy aside, I'm sure you get the idea: check the file before opening and/or sending it on to someone else. This gives you the opportunity to avoid the file altogether or at least copy and paste any vital information into a new document and send that instead.
Don't forget, if you run VirtualPC you can still become infected and lose valuable data on your Mac even though technically you're running Windows inside a sandbox. VPC will run any application you tell it to, virus or no virus, it doesn't know the difference. You can protect yourself slightly by not using VPC's 'shared folders', but that's a useful feature which you shouldn't have to be without.
Version 1.0.1 - 18 July 2005
Install buttons work for all languages
ClamXav Sentry's abort function now works properly
ClamXav Sentry's 'Launch ClamXav' menu item now works regardless of ClamXav location
Added '--quiet' switch to freshclam's cron item
Added Norwegian translation - thanks to Jo Daniel Aleksandersen
Added Turkish translation - thanks to Kerem Erkan
Clamxav No Longer Free
ClamXav has two tools for protecting your Mac. The first is the main ClamXav application, which scans the volumes you identify. A Source List down the left-hand side shows all the places you can. OK, I have inherited a Mac OS X 10.6 server. I just want to nuke ClamXav from the whole system, I don't want these errors in the log as I have other errors also to look at and this is just a potential problem for me. I have tried to download the latest ClamXav, I have tried to remove it, I have tried to run the un-installer. ClamXav is a virus scanner for Mac. It uses the very popular ClamAV open source antivirus engine as a back end and has the ability to detect both Windows and Mac threats. ClamXav can be setup up as passive or active: scan only the files you tell it to or your entire hard drive, whichever you prefer; you can also choose to activate Sentry to monitor your hard drive and scan new files as they arrive. ClamXav v2 still supports OS X 10.6.8+ and will continue to do so until v3 is released (no projected date). I'm not aware of any other current A-V software that still does. That being said, those pop-ups about being infected are not due to anything on your Mac.