An unknown individual used an anonymous web browsing tool often used to access the dark web to get into an email account on the Clinton family server, the FBI revealed on Friday.

Meanwhile, in another incident, top aide Huma Abedin revealed to an unidentified person that Clinton had fears she had been hacked after she received a phishing email.

The FBI disclosed the incidents, in a report on Clinton's handling of classified information on Friday.

According to the FBI's review of the Clinton server logs, an unidentified person accessed an email account on January 5, 2013, using three IP addresses that are known to serve as encryption tool Tor 'exit nodes'.

An unidentified person accessed an email account on the Clinton's private server from an IP address associated with encryption tool Tor in 2013

The 'exit nodes' are known jumping-off points from Tor - an encrypted privacy tool that is used to hide a person's history - to the public internet.

But the owner of the email account, whose name is redacted in the report, said she was 'not familiar with nor [had] she ever used Tor software', according to Politico.

This appears to be the first confirmed intrusion into a piece of hardware associated with Clinton's private email server.

Less than a month after the intrusion, Clinton left the State Department.

Tor is used around the world, and allows uses to hide their location and browsing habits from others, allowing them to communicate anonymously on the internet.

This gives activists, journalists and others the opportunity to use the web without interference of oppressive regimes.

But the tool, which was developed with the support of the US government, has drawn criticism by many for allowing hackers and criminals to evade law enforcement in the dark web.

The tool also is a way for users to sell porn, drugs and stolen data while covering their tracks.

In another incident that raised hacking fears, Clinton received a phishing email, purportedly sent fron the personal email account of a State official,

She responded to the email: 'Is this really from you? I was worried about opening it!'.

In a separate incident, Abedin sent an email to an unidentified person saying that Clinton was worried 'someone [was] was hacking into her email'.

She had apparently received an email from a known associate 'containing a link to a website with pornographic material' at the time, but there is no additional information as to why she would believe she had been hacked.

The FBI on Friday published interviews with Clinton and her top aides from the bureau's recently closed criminal investigation into her use of a private email server in the basement her Chappaqua, New York, home (pictured)

The FBI's report also revealed that one of Clinton's IT aides enabled Remote Desktop Protocol on the server, which made it more vulnerable to hackers.

It was revealed last year that Clinton's server, which handled her personal and State Department correspondence, appeared to allow users to connect openly over the Internet to control it remotely.

Experts said the Microsoft remote desktop service wasn't intended for such use without additional protective measures, and was the subject of U.S. government and industry warnings at the time over attacks from even low-skilled intruders.

The FBI investigators could not determine if security protocol TLS - transport layer security - was ever enabled.

In July, Director James Comey called her and her aides' conduct 'extremely careless'.

The FBI on Friday published scores of pages summarizing interviews with Clinton and her top aides from the bureau's recently closed criminal investigation into her use of a private email server in the basement her Chappaqua, New York, home.

Clinton told the FBI she never sought or asked permission to use a private server or email address during her tenure as the nation's top diplomat, which violated federal records keeping policies.

The Democratic presidential nominee has repeatedly said her use of private email was allowed.

But over three-and-a-half hours in an interview in July, she told FBI investigators she 'did not explicitly request permission to use a private server or email address', the FBI wrote.

The bureau said no one at the State Department raised concerns during her tenure, and that Clinton said everyone with whom she exchanged emails knew she was using a private email address.

The documents also include technical details about how the private server was set up. It is the first disclosure of details provided by Bryan Pagliano, the technology staffer who set up and maintained Clinton's IT infrastructure.