Booz Allen Hamilton, the vast United States contractor at the center of recent high-profile disclosures of classified information, said Thursday that it was under criminal and civil investigation for possible billing irregularities.

The consulting company said on its website that the Justice Department had informed the firm on June 7 that investigators were reviewing “certain elements of the company’s cost accounting and indirect cost charging practices with the U.S. government.” Booz Allen, considered the most profitable spy organization in the world, has lucrative contracts with the federal government that account for 97 percent of the company’s business.

After the announcement, the company’s stock price dropped more than 13 percent in after-hours trading.

Consulting firms charge the federal government for direct costs, which include a contractor’s salary, and indirect costs, such as equipment, marketing expenses and office space. Booz Allen said the investigation involved indirect costs but did not say whether it pertained to a specific government contract.