A U.S. investigation into a leak of hacking tools used by the National Security Agency is focusing on a theory that one of its operatives carelessly left them available on a remote computer and Russian hackers found them, four people with direct knowledge of the probe told Reuters.
The tools, which enable hackers to exploit software flaws in computer and communications systems from vendors such as Cisco Systems and Fortinet Inc, were dumped onto public websites last month by a group calling itself Shadow Brokers.
The public release of the tools coincided with U.S. officials saying they had concluded that Russia or its proxies were responsible for hacking political party organizations in the run-up to the Nov. 8 presidential election. On Thursday, lawmakers accused Russia of being responsible.
Various explanations have been floated by officials in Washington as to how the tools were stolen. Some feared it was the work of a leaker similar to former agency contractor Edward Snowden, while others suspected the Russians might have hacked into NSA headquarters in Fort Meade, Maryland.
But officials heading the FBI-led investigation now discount both of those scenarios, the people said in separate interviews.
NSA officials have told investigators that an employee or contractor made the mistake about three years ago during an operation that used the tools, the people said.