He and 10 others were charged last year with (Editor's Note: See  Graphic on Right)  being part of a ring of thieves from around the world that broke into nine major US retailers' computers systems, stealing customer data and then selling that information. The thieves allegedly hacked into the systems and installed programs to capture data.

Yastremskiy, according to prosecutors, earned more than $11 million from his illicit activities. He has also been charged in another US case, involving theft of data from a Texas restaurant chain.

Court documents indicate that in TJX's case, as many as 100 million card numbers were stolen. Prosecutors alleged the ringleader was Albert Gonzalez of Miami.

A 27-year-old business school graduate, Yastremskiy was arrested in 2007 while on vacation in the Turkish resort of Kemer. His attorney, Ridvan Yildiz, said he was charged with breaking into Turkish bank accounts electronically, to which he pleaded not guilty.

He was sentenced yesterday in Antalya, a city on Turkey's southwestern Mediterranean coast near the resort town.

Before sentencing, Yildiz said, Yastremskiy told the judge: "I am innocent. I didn't do anything to break bank accounts. Somebody else did it, not me. I want to be released from the jail."

Yastremskiy had also argued that a laptop computer found in his hotel room containing bank information belonged to a friend.

Yildiz plans to appeal the sentence to Turkey's highest court, known as the Yargitay.

The 30-year sentence was at the low end of the range of 24 to 72 years sought by prosecutors.

Mark Rasch, a former federal prosecutor and computer-crimes expert in Bethesda, Md., said the sentence was the longest he had ever heard of involving a cybercrime. It would be allowed under US laws only if the offenses had led to death or other extreme consequences, he said.

Yet the heavy sentence could give US prosecutors influence in obtaining Yastremskiy's cooperation against others. "This would be great leverage," Rasch said.

A previous defense attorney for Yastremskiy had said that US officials have sought to extradite him, but that Turkish law prevents that until after he serves his sentence.

Yesterday, US Justice Department officials would only say they continue to seek Yastremskiy his extradition. US prosecutors in Boston have already won several guilty pleas from minor figures in the case.

Ross Kerber can be reached at kerber@globe.com. Kerber reported from Boston. Kesler, a correspondent for the newspaper Milliyet, reported from Istanbul