A very nice technical write-up: http://mtc.sri.com/Conficker/
Yet another Conflicker (Downadup) variant, Conficker B++, has been found in the wild. The new update permits the authors of the worm to distribute updates from any website on the internet as opposed to only those on the pre-programmed update site list.
Virus authors have released a new variant of the infamous Conficker (Downadup) worm with enhanced auto-update features.
The changes in the new strain of the malware, dubbed Conficker B++, make it possible for malware authors to push out new code without publishing it on pre-programmed sites, as with earlier variants. The earlier approach has been frustrated by the recent formation of an alliance led by Microsoft geared up to block and take down sites associated with the worm.