Citing law enforcement and congressional sources, CNN reported Friday an unidentified contractor working for the agency left a pouch containing two computer backup tapes bearing the sensitive data on a train in Washington's Metrorail subway system in February 2008. One source said the tapes have yet to be recovered despite a thorough search.
The tapes were being taken from Secret Service headquarters in Washington to a since-shuttered data facility in Maryland.
A congressional source said the matter is being handled by the Department of Homeland Security's Office of Inspector General, which had no comment, CNN said.
"Some of the information could cause lives to be at risk, if someone wanted to get at the families of a high-level government worker or someone they perceived as being someone who could work against, say, a terrorist cell," said Eric O'Neill, a former FBI counterespionage agent.
The Secret Service, in a statement acknowledging the loss of the pouch, disagreed.
"These back-up tapes were not marked or identified in any way and were protected by multiple layers of security," it said. "They could not be accessed without the proper equipment, applications and encoding."
CNN said it was unclear whether the tapes were encrypted.
O'Neill, now a partner at the security firm The Georgetown Group, said even if encrypted, with new technology developed in the past five years, the tapes "could be cracked in moments."