The hack of an unknown hacker using the moniker Kahoot Hack, used by the hacker group Anonymous to leak personal information, has only been publicly revealed for the first time on Monday.
It was first reported by the New York Times on Sunday.
The New York City-based company, which has been at the center of a wave of cyberattacks against the U.S. government, said in a statement that it has not been hacked.
The company also said that it is working with law enforcement to identify the hacker.
The Times said that the hacker is believed to be an Israeli national with links to Anonymous, and the group is not a foreign government or a state.
The hack came less than a week after hackers claiming to be affiliated with Anonymous, also known as the hacktivist collective Anonymous, attacked U.K.-based IT company VMware and the White House.
The hackers targeted the White Houses Office of Personnel Management (OPM), which oversees federal government contractors.
The attack has exposed vulnerabilities in OPM, which was hit with a massive breach in 2015 that exposed the personal information of roughly 30 million federal employees.
The breach, which also included personal data of more than 10 million government employees, prompted President Donald Trump to announce a sweeping reorganization of federal government agencies.
It has also exposed weaknesses in the cybersecurity systems of major government agencies like the Federal Reserve, the Department of Homeland Security, and Department of Defense.