Hillary Clinton's closest aide was shocked to learn that hackers were trying to penetrate the then-secretary of state's private email server in 2011, according to an email the FBI recently declassified and quietly released online.

'omg,' Huma Abedin wrote Clinton IT aide Justin Cooper on January 9, 2011, after he told her that he was forced to temporarily pull the server's plug because of a breach attempt.

The document is part of a 277-page file that also includes detailed notes from an FBI agent's interview with Cooper, who admitted that doors to the 'secure' rooms installed in the Clintons' homes in Chappaqua, New York and Washington, D.C. were sometimes left open – along with safes inside.

The file reveals that the FBI this year lost its notes of a 2015 meeting with the Intelligence Community Inspector General on an unspecified Clinton-linked topic, and that Clinton's aides at one point 'lost most of' the emails related to her private server as she transitioned out of the State Department.

Cooper, who set up the server, admitted in the same interview that as Clinton was transitioning out of the State Department to private life in 2013, her staff 'lost most of' the emails related to the 'clintonemail.com' domain where her messages had been stored.

The 'omg' episode came after Cooper notified Abedin on a Sunday night that the domain's server would be offline until the following day.

'I had to shut down the server,' he wrote. 'Someone was trying to hack us and while they did not get in i didn't want to let them have the chance to.'

Huma Abedin, a longtime confidant of former Secretary of State Hillary Clinton, reacted with horror in 2011 at news that the Clinton family's private email server was the subject of hacking attempts; she's pictured last year in New York City

Clinton's unsecured server, where government email messages from her Blackberry were stored for four years, was regularly the target of foreign hackers – and contained hundreds of classified documents

Abedin sent an 'omg' message to Clinton IT guru Justin Cooper in January 2011 after he told her that he had to 'shut down the server' because it was under attack

The next morning Abedin alerted top State Department deputies Jake Sullivan and Cheryl Mills: 'Don't email HRC [Hillary Rodham Clinton] anything sensitive. I can explain more in person.'

That suggests Clinton's staff was in the habit of sending sensitive materials to her, outside of the government systems that protect officials from prying spies.

Abedin was Clinton's longtime personal aide, a deputy chief of staff at the State Department and later deputy campaign director for her ill-fated 2016 White House run.

Like Clinton, she had a 'clintonemail.com' address. The pair also shared marital troubles in common: Bill Clinton's legendary extramarital conquests, and the criminal teen sexting saga involving Abedin's ex-husband Anthony Weiner.

The hacking attempt, one of many during the years Clinton kept both her government and personal correspondence on an unsecured email server – including hundreds of classified documents – was described publicly in 2016.

But Abedin's horror at the news has gone unreported.

It's recorded in a single email, one of 277 pages of materials that turned up on the FBI's Freedom of Information Act file server in the past 72 hours.

An FBI agent's hand-written notes from a March 2, 2016 interview of Justin Cooper shows the Clinton IT expert said the 'Sensitive Compartmented Information Facilities' (SCIFs) in both of the Clintons' houses sometimes had 'open door[s],' even when Clinton wasn't there; he also said the SCIFs had safes, but he had 'no understanding' of when they would be open or closed

The same agent noted later in the interview with Cooper that he said there was a door with a 'metal key code' on the SCIF at the Clintons' D.C. home, but it was 'not always locked'

The FBI's 'vault' web page, where it distributes FOIA materials that attract wide public interest, listed parts '1 of 32' through '31 of 32' of its publicly releasable documents on Tuesday morning.

It's unclear why part 32 has been hidden, but it lives on the same file server where the thousands of other pages reside.

The newly released PDF file includes an agent's hand-written notes from interviewing Cooper, who described Sensitive Compartmented Information Facilities (SCIFs) installed at the Clintons' two homes.

At the D.C. house, the notes relate, Cooper said the SCIF was a 'small office converted by the DoS [Department of State],' and that he had removed its door to replace it with a 'temp door w/ [a] metal key code.'

The agent wrote next that the door was 'not always locked.'

The agent noted earlier in the March 2, 2016 interview that the SCIF at the Chappaqua home shared the same problem.

'Open door – not always secured, sometimes when HRC not @ residence was not closed,' he wrote, adding '(both resid[ences].'

He also noted that Cooper told him there were 'safes in SCIF' but that he had 'no understanding of when [they were] open/closed.'

The agent's notes about the SCIFs' open safes never made it into his dictated report on the Cooper interview, which the FBI transcribed five weeks later.

The lax security at the Chappaqua home could be problematic because Bill Clinton was in the habit of entertaining guests while his wife was in Washington. Secret Service agents gave one, socialite Julie Tauber McMahon, a free pass to come and go as she pleased.

They nicknamed her the 'Energizer' for her frequent rendezvous with the former president, a reference to the indefatiguable mechanical bunny in TV ads from the 1980s.

The Clinton email saga gripped the nation's attention for most of the presidential general election season, until the FBI's then director James Comey closed the file in July 2016 without charging her with mishandling classified information.

Although foreign intelligence services tried to gain access to the Clinton server, it's not clear whether they ever succeeed. Far more damaging was a successful hack on her campaign chairman John Podesta's Gmail account, a move that put thousands of pages of embarrassing material on display via a release by WikiLeaks.

The newly available documents from the FBI describe an episode from 2013, when Clinton was transitioning out of her job as America's top diplomat.

These declassified pages show an episode three months ago where the FBI was unable to find notes from a meeting with the Intelligence Community Inspector General about an unspecified topic that was related to Clinton

The data from her server was at the same time being moved to Platte River Networks, a small IT firm in Colorado.

In order to 'formalize [a] new office' for Clinton and 'set up staff accounts,' Cooper said, he needed a new email domain.

That, he said, meant the 'clintonemail.com' domain was 'going away.'

In the shuffle of moving, he told the FBI agent, someone 'lost most of clintonemails.'

The State Department, the agent wrote, 'didn't have [a] system for archiving' messages.

Cooper and other IT experts 'don't know if [the] admin[istration] did [a] backup.'

When news of the private email server was first published, the State Department, then led by John Kerry, demanded its contents in order to be able to comply with future FOIA requests.

Clinton and her lawyers have said they deleted tens of thousands of those messages because they concerned 'personal' matters, not government work.

It's unclear whether the 'lost' emails from Clinton's State Department tenure were restored, whether they represent the ones Clinton said she deleted, or if there's a different explanation.

At the time, Cooper told the agent, former President Bill Clinton wanted Platte River Networks to archive the emails because they were 'good w/ tech stuff.'

The firm was later exposed as a tiny operation with little experience that kept its computer servers in a bathroom closet.

Clintonworld's inept data handling made news in 2015 when the Senate Homeland Security Committee found evidence of hack attempts on Clinton's server in 2013 and 2014.

Chairman Ron Johnson, a Wisconsin Republican, revealed his correspondence with a Florida-based computer security firm that first flagged the attacks.

Internal Clinton emails cited in one letter suggested that the now-infamous server went at least three months without any kind of threat-detection system before the Clintons hired the company.

President Donald Trump made the server's lack of data security a major issue in 2015 and 2016, mocking how Clinton commingled classified material with ordinary emails, demanding to know where her deleted messages were, and sparking chants of 'Lock Her Up!' after the FBI declined to prosecute.

The political chronicle gave birth to hundreds of FOIA requests, including one for which the FBI sought notes of a 2015 meeting with the Intelligence Community Inspector General.

Three pages from Tuesday's release describe the FBI declaring the notes 'missing' and an agent noting that the event concerned the 'MYE,' or 'Mid-Year Review,' the Bureau's unofficial nickname for the Clinton probe.