Flashback is the latest attempt to infiltrate Macs as of April 7, 2012.
Apple has posted a knowledgebase article about it.
Until all known varients of the malware have been diagnosed, you are probably better off with ClamAV. to ensure you catch all known variants.
A test of whether or not you have the malware is available with a simple script from one of the other volunteers of the forum, etresoft:
This test has no assurance of catching all known variants, but it is better than none, or trying to keep up with anti-virus software.
If you have been infected it may give you additional false positive info in addition to the accurate indication you have been infected. So ask on the forum first whether or not the info is false or not, based on the results you get. Don't jump to conclusions that every positive report means a file needs to be deleted.
Note turning off Java on your web browser while it may help prevent the infection from spreading is not a bulletproof method. If you have issues
that appear to be caused by it, be sure ask on the forum, and wait for someone who has a balanced approach to respond to your post. Don't panic!
There is also a blog that is very thorough and in plain English explains how to both detect and eradicate the malware:
Note: Only for those who know the Terminal inside out, I provide these links from f-secure:
It is described here http://www.f-secure.com/v-descs/trojan-downloader_osx_flashback_i.shtml
And further reference is on http://www.f-secure.com/v-descs/trojan-downloader_osx_flashback_k.shtml