Clearspace (just like Jive Forums) uses ICAP compatible virus scanners, you find out more about virus scanning configuration from the Jive Forums documentation:
I was about to post the same question. Could you add the word ICAP to the "Virus Scanner" page?
Most vendors offer an ICAP interface for their AV solution. I found this nice datasheet a few days ago: http://us.trendmicro.com/imperia/md/content/us/pdf/products/enterprise/interscanwebsecuritysuite/datasheet_-_linux.06iwss.pdf