A U.S. grand jury has indicted five members of the Chinese military for allegedly cyber spying on American companies in the nuclear power, metals and solar products industries, the Department of Justice said on Monday.

The military hackers conspired to steal information that would be useful to competitors of those companies in China, including state-owned companies there, the agency said.

Six American companies, including United States Steel Corp, Alcoa Inc and Allegheny Technologies Inc, and one labor union were victims of Chinese hacking attacks, U.S. officials said.