(Bloomberg) -- A 17-year-old recent Florida high school graduate pleaded not guilty to charges that he hacked more than 100 high-profile Twitter accounts as part of a cryptocurrency scam by duping the social media company’s employees.

Graham Ivan Clark was charged last week with posting messages on behalf of notable businesspeople, celebrities and politicians, including former president Barack Obama, Amazon.com Inc. Chief Executive Officer Jeff Bezos and Tesla Inc. CEO Elon Musk, and luring additional victims into sending him Bitcoin donations of more than $100,000. Two others were charged with helping Clark by serving as brokers on the sale of compromised accounts.

Clark entered the plea to more than 30 charges filed against him on Tuesday morning in Florida state court in Tampa before Judge Christopher Nash, according to court records. He is scheduled to appear again on Wednesday for a hearing on his request to change the amount of his bail bond and the conditions of his release.

The defendants were allegedly part of an underground subculture of hackers dedicated to stealing, buying and selling online accounts with desirable user names. Clark is accused of gaining access to the accounts by convincing Twitter employees that he was a colleague who needed log-in credentials to access the company’s customer-service platform.

The July 15 hack, the highest-profile security breach in Twitter’s history, forced the company to temporarily limit access to its internal tools while it investigated the intrusion and acknowledge that employees were fooled into sharing sensitive information over the phone.

Read More: ‘Mastermind’ Accused of Twitter Hack Just Out of High School

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