Hmmmm... One of the comments at the "Clam" page is rather negative. I don't have an axe to grind, just saying... And I don't particularly agree with the assessment regarding Intego either.
I installed iAntiVirus and one thing that I like about it is the handy icon in the Finder Menu Bar.
Choosing whether or not to run anti-virus software sure was easier in the pre-OS X days...