FireEye shares tumble after company cuts forecasts

(Reuters) - FireEye Inc shares tumbled nearly 18 percent on Thursday after the cyber security firm missed quarterly forecasts and cut its revenue outlook, saying that a reduction in cyber spying from China had hurt demand for its products. Wall Street analysts and industry watchers said that they were sceptical of FireEye's assertion that a U.S.-China agreement to clamp down on hacking had hurt sales of the cyber security firm, at a time when corporations are placing unprecedented attention on e