the last I heard, rather, actually read on someone's posting here in the Apple Discussions, was that clamav virus definitions were sorely out of date for Mac DNS Changer trojan variants, only having the original RSPlugA definitions. That was a few months ago, and I have subsequently read somewhere else that Mark Allen, maker of the clamXav GUI front-end for clamav, was working, or attempting to work, with someone at clamav who actually cared, if he could find such an individual. But I don't know anything beyond that. For now, I, personally, only trust clamav to keep me from passing Windoze malware on to my Windoze-using friends.
I also read, I believe in the Apple Discussions, that the free DNS Changer Removal was not detecting the later variants of this DNS Changer trojan, but that the company who makes it, had incorporated all the latest definitions in its macScan product (this latter presumption of mine is based on
this thread). Seems like macupdate and versiontracker give iAntivirus good marks, too. macScan's, I think, are lower overall because a lot of people "dissed" them early on in that product's life, because "there (was) no malware for Macs." But that's changed now, and I think macupdate/versiontracker raters are giving much higher marks for macScan now, too. I believe both of these products are still "subscription-free" unlike their 800-lb-gorilla competition.