BOSTON - A Ukrainian man recently arrested in Turkey is suspected of selling some of the credit and debit card numbers stolen in a data hack of at least 45 million cards of TJX Cos. retail customers, a U.S. investigator said yesterday.

Authorities hope the arrest of Maksym Yastremskiy, suspected of being a major international trafficker in stolen data, will eventually lead to information uncovering the TJX intruders' identities.

"He was involved in the distribution of information," Greg Crabb, an agent with the U.S. Postal Inspection Service's global investigations unit, told The Associated Press. "We do have information that suggests other individuals were the masterminds of the hack."

U.S. investigators' interest in Yastremskiy in connection with the TJX case was first reported yesterday in The Boston Globe. The 24-year-old was arrested weeks ago in the Turkish resort city of Kemer.

Yastremskiy's capture follows the arrests in Florida of 10 people accused of using stolen TJX customer data to buy Wal-Mart gift cards, though they also aren't believed to be the TJX hackers. Several have entered guilty pleas in recent months.

Crabb said information from Turkish officials holding Yastremskiy indicates he was a major trafficker in stolen data from sources including TJX.

"At one particular instance, he had solicited the sale of over a million credit card numbers," Crabb said. "To be able to gain access to that much data, you've got to have a good source."

Crabb said information from credit card issuers pointed to Yastremskiy as the source of illegally trafficked data stolen in the TJX case. Card numbers were allegedly trafficked online and internationally, as is common in identity theft cases that frequently stretch across the globe and often involve Eastern Europe.

Officials from the U.S. Secret Service and Department of Justice, which also are investigating the TJX case, declined to comment Tuesday, as did a spokeswoman for Framingham, Mass.-based TJX.

TJX, the owner of 2,500 discount retail stores worldwide including T.J. Maxx and Marshalls, disclosed the breach on Jan. 17, and said March 28 that one or more intruders unearthed data from at least 45.7 million credit and debit cards from transactions as long ago as early 2003.

Independent organizations that track data thefts say the TJX case is believed to be the largest in the United States based on the number of customer records compromised.

TJX says about three-quarters of the 45.7 million cards had either expired by the time of the theft, or the stolen information didn't include security code data from the cards' magnetic stripes. However, TJX also has said the intruders could have tapped the unencrypted flow of information to card issuers as customers checked out with their credit cards.