Since its arrival, there have been several variants of the Conficker worm. They can all be referred to as the Conficker family of malware. These variants have improved upon Conficker's code and have been released in response to attempts to stop or remove Conficker's infestation. It should also be noted that Conficker.D does not spread by attacking new systems and just updates existing Conficker.C infected machines. See Appendix B, which contains a listing of links to Microsoft's Security Portal Threat Encyclopedia, for a full discussion of the variants of Conficker