ClamXav is a free virus scanner for Mac OS X. 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.

Introducing ClamXav 2

  • Clean, simple-to-use interface
  • Clearly lists infected files
  • Free virus definitions (usually updated daily)
  • Save your favourite scan locations for easy access
  • Customise the toolbar - or hide it entirely
  • Send selected files to quarantine or trash with one click
  • Specify files to exclude using plain text* or by using drag & drop from the Finder
  • Specify schedules to update virus definitions and perform scans
  • Use ClamXav Sentry to monitor your hard drive and scan new files as they arrive†
  • Use the bundled ClamAV engine or bring your own installation†
  • Compatible with Mac OS X 10.5, 10.6 and 10.7 Lion
source: http://www.clamxav.com/