Conficker - also known as Downup, Downadup and Kido - is a Windows worm that targets flaws in the operating system to co-opt machines and link them into a virtual computer that can be commanded remotely by its authors.
The Conficker worm uses a combination of advanced malware techniques which has made it difficult to counter, and since appearing last November has spread rapidly into what is now believed to be the largest computer worm infection since the SQL Slammer of 2003.
According to the Shadowserver Foundation, a volunteer group of IT security professionals, the Conficker worm is still very common in Brazil and China.
Interestingly, the foundation said that it has been able to keep track of Conficker worm infections by cracking the algorithm the worm uses to look for instructions on the internet and placing their own 'sinkhole' servers on the domains it is programmed to visit.
Infosecurity notes that, despite the size of the botnet, Conficker has only rarely been used by the criminals who control it, although no reason has been put forward by security experts as to why this should be the case.