(CNN) The University of California is making a series of changes to help combat fraud after an admissions scandal involving several colleges nationwide.

Fifty people -- including Hollywood stars, top CEOs, college coaches and standardized test administrators -- allegedly took part in the scheme to cheat on tests and admit students to leading institutions as athletes regardless of their abilities.

William Rick Singer, the plot's purported mastermind, allegedly told prospective clients that he created a "side door" for wealthy families to get their children into top US colleges, and parents paid him millions of dollars, authorities said.

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Singer has pleaded guilty to racketeering conspiracy, money laundering conspiracy, conspiracy to defraud the United States and obstruction of justice. He is due to be sentenced in September.

Several universities were caught up in the scandal, including Stanford , the University of Southern California, UCLA and Georgetown University.

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