WASHINGTON — Law enforcement faces an “enormous challenge” in preventing state-sponsored cyber crimes, FBI Director James Comey said today, days after the Justice Department charged five Chinese military officials with hacking into American companies — most of them with Western Pennsylvania connections — to steal trade secrets.

“There are two kinds of big companies in the United States: those who’ve been hacked by the Chinese and those who don’t yet know that they’ve been hacked by the Chinese,” Comey told the Senate Judiciary Committee.

“It’s a problem,” he added, “that we are responding to with a lot of energy, working with a lot of partners across the government.”

He said the increased focus on cyber security has heightened the FBI’s demand for new, tech-savvy experts.