An unknown individual using the encrypted privacy tool Tor to hide their tracks accessed an email account on a Clinton family server, the FBI revealed Friday.

The incident appears to be the first confirmed intrusion into a piece of hardware associated with Hillary Clinton’s private email system, which originated with a server established for her husband, former President Bill Clinton.

The FBI disclosed the event in its newly released report on the former secretary of state’s handling of classified information.

According to the bureau’s review of server logs, someone accessed an email account on Jan. 5, 2013, using three IP addresses known to serve as Tor “exit nodes” — jumping-off points from the anonymity network to the public internet.

The owner of the account, whose name is redacted in the report, said she was “not familiar with nor [had] she ever used Tor software.”

Clinton left the State Department less than a month after the intrusion.

Tor, developed with support from the U.S. government, is used around the world to let people such as activists and journalists communicate and surf the Web without interference from oppressive regimes, but it has also drawn criticism for allowing hackers and criminals to evade law enforcement while peddling porn, drugs and stolen data.

The new report also revealed that one of Clinton’s IT aides enabled Remote Desktop Protocol on the server, despite known vulnerabilities in the protocol. FBI investigators also could not determine if the widely recommended security protocol TLS was ever enabled.

The FBI in July declined to recommend charges in connection with Clinton’s email practices, though Director James Comey called her and her aides’ conduct “extremely careless.”