This special variant further uses another obfuscation technique for cases where it fails to find a live update point. In order to make sure the botnet always ‘calls home’ Zeus’s operators programmed a randomized, on-the-fly domain name generator, based on a constant algorithm the Trojan’s configuration dictates. The algorithm creates 1,020 domain names URLs per day. Each new and unique domain name is a string of letters. The suffix “/news” or “/forum” follows the domain name when it is used for the Trojan’s update and drop communications.

via Organized Cybercrime: Nefarious Sophistication Featuring Zeus V2.1.0.10 « Speaking of Security – The RSA Blog and Podcast.