The world of hackers can be roughly divided into three groups. “Black hats” break into corporate computer systems for fun and profit, taking credit card numbers and e-mail addresses to sell and trade with other hackers, while the “white hats” help companies stop their disruptive counterparts. But it is the third group, the “gray hats,” that are the most vexing for companies. These hackers play it any number of ways, which can leave a company vulnerable to lost assets as well as a tarnished reputation as security breaches are exposed. (The terms are a nod to westerns, with the villain wearing ...