When it comes to industrial espionage, "one-hit wonders" -- employees such as Chelsea Manning or Reality Winner who take valuable proprietary information to a competitor, the media or a foreign government -- are just half of the equation. Companies also need to remember the threat of low-key spies on staff who may quietly provide their handlers with sensitive facts and figures over months, years and even decades. The damage these employees can cause may rival, or exceed, the harm caused by a one-time loss....