SEATTLE — Boeing is investigating an internal security breach impacting thousands of workers in four U.S. states, including Washington.

The company says it was notified in January after a worker accidentally sent personal information of 36,000 Boeing employees to his spouse in November, according to KOMO-TV.

The worker told investigators he needed help formatting a spreadsheet and didn't realize the document contained sensitive information.

Boeing says the spreadsheet contained employee names, ID numbers and accounting codes in visible columns and birth dates and Social Security numbers in hidden columns.

The company sent a letter to Washington Attorney General Bob Ferguson in February informing him of the breach impacting 7,288 Boeing employees there.

Boeing sent a letter to workers who may have been affected and offered free credit monitoring.

Boeing says copies of the spreadsheet have been destroyed and they don't believe personal information was misused.