“In order to infiltrate those organizations you have to be established,” Mr. Magaw said. “You cannot just get on criminal boards and start dealing with high-level players. He provided us with that ability to do that on Shadowcrew.”

In the wake of Operation Firewall  and the expanding wave of credit card theft emanating from south Florida  the Secret Service began to focus on how the members of Shadowcrew and other carders were obtaining stolen credit card data.

They focused on a ring of people, most of whom had never met in person, who were working together in cyberspace and breaking into corporate computer systems nationwide.

Secret Service agents from the San Diego field office homed in on Maksym Yastremskiy or “maksik,” 25, from the Ukrainian industrial city of Kharkiv. Agents believed that he was among the largest distributors of stolen debit and credit card numbers in the world. Mr. Yastremskiy, an indictment unveiled last week in San Diego alleges, earned over $11 million plying his trade in 2004-6 alone.

In July 2007, the Secret Service learned that Mr. Yastremskiy was traveling on vacation to Turkey and the agency coordinated his arrest by the Turkish police outside a nightclub in Kemer. The Turkish police provided a copy of the hard drive from Mr. Yastremskiy’s laptop to Secret Service agents, yielding significant breakthroughs in the case.

In addition to millions of stolen credit and debit card numbers, investigators found a sniffer program similar to the one used that year to capture credit card transactions at 11 restaurants in the Dave & Buster’s chain. That attack, unlike earlier ones, was not conducted through war-driving. Instead, Aleksandr Suvorov, 24, an Estonian hacker, remotely accessed the chain’s computers by exploiting errors in the way it set up passwords, investigators say.

Agents brought the sniffer program to the Computer Emergency Response Center at Carnegie Mellon University, where experts compared it with another program found during the investigation of the earlier breach at TJX and found they were two versions of the same underlying code. Agents now knew conclusively that the same gang was responsible for both crimes.