WASHINGTON, Aug 28 (Reuters) - Credit bureau TransUnion ( TRU )

said Thursday that more than 4 million people's data was exposed

in a recent hack involving an unidentified third party.

In a letter dated earlier this week and posted to the

website of Maine's attorney general, the company said it had

"recently experienced a cyber incident involving a third-party

application serving our U.S. consumer support operations."

In a statement, TransUnion ( TRU ) said it had "quickly contained

the issue, which did not involve our core credit database or

include credit reports."

Maine legally requires disclosures for certain kinds of

breaches affecting its residents. The name of the third party

application was not disclosed, but U.S. corporations have

recently seen waves of compromises as hackers trick employees

into opening up their respective employers' Salesforce

databases.

A Salesforce representative did not immediately return a

message seeking comment.