FBI investigation of leaked NSA hacking tools examines operative's 'mistake'

As explanations swirl in Washington for how tools were stolen, sources say an agent, an unsecured computer and Russian hackers are the focus

A careless agent. A cache of hacking tools left on a remote and unsecured computer. A shadowy group of Russian hackers. A fire-sale on the deep web.

This is the current focus of a inquiry into a cache of NSA exploits that were dumped on to public websites last month by a group calling itself the Shadow Brokers, four people with direct knowledge of the probe investigation told Reuters.