A former McKinsey & Co director charged with leaking confidential information to Galleon Group founder Raj Rajaratnam became the seventh person to plead guilty in what U.S. prosecutors have called the biggest hedge fund insider trading case ever.

Anil Kumar pleaded to securities fraud and conspiracy charges in Manhattan federal court on Thursday, after last month having been let go by McKinsey, a consulting firm.

Kumar, 51, has been free on $5 million bail since his October 16 arrest. He could face as many as 25 years in prison.

According to U.S. prosecutors and a civil complaint by the U.S. Securities and Exchange Commission, Kumar in August 2008 shared inside information about transactions involving Advanced Micro Devices Inc and two Abu Dhabi entities with Rajaratnam, who then traded on the information.

On October 7, 2008, AMD said it would spin off manufacturing operations through a multibillion dollar venture with the Advanced Technology Investment Co of Abu Dhabi.

AMD stock opened 25 percent higher that day, resulting in millions of dollars of illegal profits for Rajaratnam, Kumar and others, prosecutors said.

Twenty-one people, including employees of some of America's biggest companies including IBM Corp and Intel Corp , have been criminally or civilly charged in the sprawling case.

Rajaratnam, a Sri Lankan-born U.S. citizen, has pleaded not guilty and vowed to fight the charges.

The cases are USA v Rajaratnam et al, U.S. District Court, Southern District of New York, No. 09-01184; USA v Goffer et al in the same court, No. 09-mj-02438, and SEC v Galleon Management LP et al in the same court, No. 09-cv-08811.

(Reporting by Grant McCool; Editing by Tim Dobbyn)