The hackers also sought to copy “certain information that was subject to U.S. law enforcement requests pursuant to court orders,” the FBI said, suggesting the hackers may have been trying to compromise programs like those subject to the Foreign Intelligence Surveillance Act, or FISA, which grants American spy agencies sweeping powers to surveil the communications of individuals suspected of being agents of a foreign power.”

The warning comes after several high-profile hacking incidents that U.S. authorities have linked to China, part of what they say is an effort to steal technological and government information while also targeting vital infrastructure like the electrical grid.