For the past week or so, MSRC has been closely tracking a new family of threats called Stuxnet (a name derived from some of the filename/strings in the malware — mrxcls.sys, mrxnet.sys).  In the past few days, it has become a  popular topic of discussion amongst security researchers and in the media. First and foremost, MSRC has recently released one additional signature for this threat, and urge our readers to be sure that you've got the latest anti-malware definition updates installed.

http://blogs.technet.com/b/mmpc/archive/2010/07/16/the-stuxnet-sting.aspx

Urs