Information from Hillary Clinton's unauthorized, private email server were found on the dark web, newly released documents from the FBI show.

It has long been suspected that Clinton's server, located in her home in Chappaqua, N.Y., might have been breached by hackers, but that has never been publicly confirmed.

But notes from a independent review, obtained by the FBI and released from "The Vault" on Friday, determined the Romanian hacker known as Guccifer breached a server for Clinton ally Sidney Blumenthal, who was passing information about Libya to the secretary of state, and Clinton's server was "indirectly" hacked likely as a result of the breach of Blumenthal's server. This information was transferred to a computer or network located south of Bucharest, Romania. The report said a second indirect hack of Clinton's server by people working on Guccifer's behalf took place on May 22, 2009, followed by other breaches.

The study found Guccifer used an anonymous server in Russia to carry out the "penetration" and there was a "high possibility" that Russian services monitored these servers and might have a copy.

One file taken from Clinton's server that was not seen on Blumenthal's server was found on the deep web, a hidden layer of the Internet not indexed by search engines, and the dark web, a shady constellation of darknets with layers of encryption favored by cybercriminals and hackers.

It is described as an Excel spreadsheet with "targeting data" that would receive the highest level of classification. "If it is determined by the by the FBI that this file ever was overtly classified, it will serve as a potential 'smoking gun document,'" the notes said.

"This file represents a major loss to the Intelligence Community because it appears to be targeting data," the notes said. This file was translated from Russian to Arabic, represented a list of targets "possibly" created by a Russian source, "located or intercepted by our services," and was sent to Clinton by an unknown individual, the notes said.

Guccifer was found to have penetrated "a number of targets" and 37,000 files were found on a computer traced to an IP address he obtained.

The study was conducted by a vendor hired by conservative watchdog group Judicial Watch due to concerns that Clinton's server had been hacked. The bureau obtained the report during an interview with the vendor, which is shown in the documents released Friday.

Guccifer, whose real name is Marcel Lazar, has been serving prison time for hacking charges since 2014, both in the U.S. and in his native Romania.

It has been known that he successfully hacked Blumenthal, a breach that led to the first revelation of Clinton's use of the private clintonemail.com domain.

Guccifer was convicted on charges of hacking more than 100 prominent Americans, including former secretary of state Colin Powell and a sister to former President George W. Bush. He had claimed to hack Clinton during her term as secretary of state, though he was never charged with doing so.

An online persona known as Guccifer 2.0 claimed to be the hacker behind the breach of the Democratic National Committee computer network during the 2016 election. Guccifer 2.0 gave stolen emails from Democrats to WikiLeaks, which then published them. Special counsel Robert Mueller determined that Guccifer 2.0 was a front operated by Russia's Main Intelligence Directorate of the General Staff, or GRU.