Serco and FRTIB were alerted in April by the Federal Bureau of Investigation that one of the computers used to service TSP had been the victim of unauthorized access. Besides shutting down the computer, FRTIB and Serco did forensic analysis to determine which people were affected, and enhanced the security, FRTIB and Serco said in separate statements. Serco confirmed that its computer had been affected.

Several files with different combinations of data of the individuals were accessed, FRTIB said. The names, addresses, and Social Security numbers of about 43,000 individuals were in the accessed files.  In some cases, this group of data also included financial account numbers and routing numbers, it added.

Another group of about 80,000 people had their Social Security numbers and some TSP-related information accessed, but their name was not associated with the information, FRTIB said.

TSP is a retirement savings and investment plan for federal employees and members of the uniformed services, administered by the FRTIB.

"There is no evidence of any funds being diverted or identity theft resulting from the incident," Serco in Reston, Virginia, said. There was also no evidence that the TSP network, which supports the savings plan's 4.5 million participants, was the victim of an unauthorized access, it added.