You can also upload the file to VirusTotal at
http://www.virustotal.com/en/indexf.html where they will scan it with about 30 antivirus engines. You will receive a report when finished. Engines that miss infected files will receive copies of the file so they can get the infection in their signature database. I'm not sure, but this may be faster than sending Clam an infected file. The Clam people send out several lists each day of submissions from VirusTotal.
VirusTotal also has a handy downloadable script to let you send them files directly from your computer via the Windows Explorer right context menu.
Regards,