Attorney General Eric Holder on Monday announced that a federal grand jury in Pennsylvania had filed criminal cyber espionage charges against five members of a Chinese People's Liberation Army hacking unit based in Shanghai.

"Enough is enough," Holder said at a Justice Department news conference, noting that the charges should serve as a "wake-up call" to cyberspies who target the U.S.

But when pressed on how the Justice Department expects to prosecute five members of the Chinese military, all Holder could say was: "You can never tell how things will play out."