Known as W32.Gammima.AG, it is a worm that spreads through removable media such as USB drives and external hard drives, and is known to steal online gamers' user names and passwords. Gamimma steals sensitive information for various online games, including ROHAN, R2 (Reign of Revolution), Talesweaver, Seal Online, and several games popular mainly in China, including ZhengTu and HuangYi Online, according to Symantec. The Gamimma worm was first discovered on August 27, 2008.
See "Password Stealing Worm Catches NASA Napping" on internetnews.com
Also see "The Difference Between a Virus, Worm and Trojan Horse" in the Did You Know?" section of Webopedia.