UPDATE 1-US Justice Dept opens IBM antitrust probe-trade group

* DOJ probe is of mainframe business

* Scope of investigation is broad

WASHINGTON Oct 7 (Reuters) - The U.S. Justice Department has opened an investigation into allegations that International Business Machines (IBM.N) abused its dominance of the mainframe business, said Computer and Communications Industry Association chairman Ed Black.

The CCIA had urged the Justice Department to open the probe, accusing IBM of anti-competitive conduct for doing things like refusing to license its mainframe operating systems to users of "Hercules" for installation on machines other than IBM mainframes.

Hercules is an open-source project that would allow IBM's mainframe operating systems to run on Intel-based (INTC.O) and Advanced Micro Devices-based (AMD.N) computers.

"We are aware that Justice has begun the CID investigatory process," said Black. A CID is the equivalent of a subpoena and indicates that an investigation is under way. "The scope is quite broad."

Neither IBM nor the Justice Department could immediately be reached for comment. (Reporting by Diane Bartz; Editing by Gary Hill)