Scam baiting is a form of Internet vigilantism where the vigilante poses as a potential victim to the scammer in order to waste their time, gather information that will be of use to authorities, or publicly humiliate the scammer. It is, in essence, a form of social engineering that may have an altruistic motive or may be motivated by malice. It is primarily used to thwart the 419 Nigerian advance-fee scam and can be done either out of a sense of civic duty or as a form of amusement.
Scam baiting is usually done simply by gaining access to an e-mail address that has already been targeted by scammers, which given the prevalence of the spam is not a difficult proposition. Once access is gained, the baiter impersonates a person that is receptive to the financial hook that the scammer is using. The objective is to keep the scam going as long as possible, costing the scammer time and energy. Secondary goals include gathering as much information as possible to share with authorities. Amusement that the baiter may gain from the interaction include fooling the scammer into falling for claims just as ludicrous as the ones that the scammer is using to bilk the victim of money. Many baiters will use joke names (Hugh Janus, Jenny Talwarts, Dick Head and so on) which while obviously ludicrous to a native or fluent English speaker will go unnoticed by the scammer. Similarly baiters may introduce characters and even plot-lines from movies or television shows for comedic effect.
http://en.wikipedia.org/wiki/Scam_baiting