"From New York to Norway and Japan to Australia, Operation Card Shop targeted sophisticated, highly organized cyber criminals involved in buying and selling stolen identities, exploited credit cards, counterfeit documents, and sophisticated hacking tools," FBI Assistant Director Janice K. Fedarcyk said in a statement. "Today's arrests cause significant disruption to the underground economy and are a stark reminder that masked IP addresses and private forums are no sanctuary for criminals and are not beyond the reach of the FBI."
Some CarderProfit users apparently learned of the involvement of the feds months ago. A Twitter user with the name @JoshTheGod wrote that "has informants and most likly to be believed as a Federal Sting," back in April.
Late update: A source sends along this screengrab of what CarderProfit.cc looked like before the FBI took it down.
Late, late update: the feds provide this explanation of how the undercover website worked:
In June 2010, the FBI established an undercover carding forum, called "Carder Profit" (UC Site), enabling users to discuss various topics related to carding and to communicate offers to buy, sell and exchange goods and services related to carding, among other things. Since individuals engaged in these unlawful activities on one of many other carding websites on the Internet, the FBI established the UC Site in an effort to identify these cybercriminals, investigate their crimes, and prevent harm to innocent victims. The UC Site was configured to allow the FBI to monitor and to record the discussion threads posted to the site, as well as private messages sent through the site between registered users. The UC Site also allowed the FBI to record the Internet protocol (IP) addresses of users' computers when they accessed the site. The IP address is the unique number that identifies a computer on the Internet and allows information to be routed properly between computers.
Access to the UC Site, which was taken offline in May 2012, was limited to registered members and required a username and password to gain entry. Various membership requirements were imposed from time to time to restrict site membership to individuals with established knowledge of carding techniques or interest in criminal activity. For example, at times, new users were prevented from joining the site unless they were recommended by two existing users who had registered with the site, or unless they paid a registration fee.
New users registering with the UC Site were required to provide a valid email address as part of the registration process. The e-mail addresses entered by registered members of the site were collected by the FBI.