WASHINGTON (AP) — Law enforcement faces an “enormous challenge” in preventing state-sponsored cyber crimes, FBI Director James Comey said Wednesday, days after the Justice Department announced charges against five Chinese military officials accused of hacking into American companies 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.