Don’t get too complacent with your security if you’re on a Unix machine. Software you download from the Internet should still be scanned. A good illustrative example is the recently discovered infection of Mozilla binaries. Now, granted, they were Korean binaries and maybe not even very popular Korean binaries, but it happened. ClamAV is free, easy to use, and self-updating. So clamscan ~/downloads once in a while, OK? (read cron)
<p>Update: The infected binaries were on a 3rd party unofficial mirror (fan site), not an official Mozilla distribution point.