A series of 'tracking dots' that were inadvertently published by The Intercept on leaked documents could have led to the arrest of an NSA contractor.

Reality Leigh Winner, 25, a Georgia security contractor with top secret clearance, was arrested and charged with leaking documents on Monday as NBC linked her to pages published by The Intercept.

Now, blog Errata Security has revealed how a series of nearly-invisible yellow dots that appeared at the top of the leaked pages would have allowed security services to track the leaker down with ease.

The leaked documents seemed to show Russia carried out cyber attacks on companies which produce software used during elections.

Reality Winner, 25, was arrested and charged for leaking classified documents on Monday as reports said she was behind information published by The Intercept

Blog Errata Security revealed how a series of nearly-invisible yellow dots at the top of the pages which appeared on The Intercept allowed the leaker to be traced

The dots (made easier to see by inverting colors on the documents) are added by virtually every modern printer to the top and bottom of every document they print

According to analysis carried out in 2015 by the Electronic Frontier Foundation, almost every modern printer secretly adds 'tracking dots' to every document.

The dots appear in a grid at the top of the first page and bottom of the last page, with some spaces filled in and others left blank.

Once flipped upside down, that pattern can be fed into software which reads it.

The software will then tell the user the exact date and time the document was printed, as well as the model and serial number of the printer it came from.

In the case of the NSA documents, that was a printer with model number 54, serial number 29535218, and the document was printed on May 9, 2017, at 6:20, Errata writes.

Because the NSA almost certainly keeps a record of all its printer serial numbers, it would have been a simple job to track the machine to Georgia.

All agents would then have to do is check who was using the printer at 6.20 on May 9 - information the NSA almost certainly keeps on record.

According to the criminal complaint, agents identified Winner after ascertaining that six people had printed the leaked information.

Once those six people had been identified, agents checked the email accounts of those staff members and saw that Winner was the only one who had emailed an outside news source.

When confronted, the report says she admitted leaking the information.

'Exceptional law enforcement efforts allowed us quickly to identify and arrest the defendant,' the arrest document said.

The dots form a grid with some squares colored in and others blank. When flipped upside down and fed into special software, this reveals when the page was printed, along with the model and serial number of the printer

Once investigators had this information, it would have been a simple job of checking with the NSA where printer 29535218 was kept and who was using it at 6.20 on May 9

Winner is the first person to be charged over leaking confidential documents after President Trump vowed a crackdown on informants.

'Winner is a contractor with Pluribus International Corporation assigned to a U.S. government agency facility in Georgia,' according to a government criminal complaint.

'She has been employed at the facility since on or about February 13, and has held a Top Secret clearance during that time.

'On or about May 9, Winner printed and improperly removed classified intelligence reporting, which contained classified national defense information from an intelligence community agency, and unlawfully retained it.'

'Approximately a few days later, Winner unlawfully transmitted by mail the intelligence reporting to an online news outlet,' according to the release.

The documents published by The Intercept seemed to show that Russia had tried hacking into software used by an election company.

'Russian General Staff Main Intelligence Directorate actors… executed cyber espionage operations against a named U.S. company in August 2016, evidently to obtain information on elections-related software and hardware solutions,' according to the document.

Winner is the first person to have been charged over leaking information to the media after Donald Trump vowed a crackdown

Winner's social media reveals she was a Bernie Sanders supporter who regularly tweeted her disapproval of the Trump administration

'The actors likely used data obtained from that operation to… launch a voter registration-themed spear-phishing campaign targeting U.S. local government organizations.'

Winner's mother, Billie Winner-Davis, said that she was shocked to learn about her daughter's arrest and that the family is not even sure why she's been arrested.

'I don't know what they're alleging,' she told told The Daily Beast. 'I don't know who she might have sent it to. [DOJ] were very vague.

'They said she mishandled and released documents that she shouldn't have, but we had no idea what it pertained to or who.'

She shared that her daughter, who had been a linguist for the U.S. Air Force and can speak middle eastern languages Farsi, Dari and Pashto, called on Sunday to ask to have her pets relocated.

Winner-Davis said that her daughter never discussed her work, and that her family didn't know much information about her job as a government contractor.

Winner was an employee at Pluribus International Corporation based out of Alexandria, Virginia. She was then posted to a government agency in Georgia. She worked at the facility since February 13, and held Top Secret security clearance.

Winner was employed by contractor Pluribus International Corporation in February, and had been working with access to top secret documents since then

A probable cause affidavit says agents 'determined six individuals printed [the confidential report]' but did not reveal how they did so

Pluribus is an analytical and engineering service that provides its services to federal, defense, security and the intelligence community on a contractual basis. The company has 22 locations across the world, including three in the Republic of Korea.

Her mother revealed that she is unsure if her daughter will be able to seek bond and that she has a hearing on Thursday.

Winner-Davis also mentioned how her daughter was quite outspoken about her beliefs.

'She's very passionate. Very passionate about her views and things like that, but she's never to my knowledge been active in politics or any of that,' Winner-Davis stated.

However, a Twitter account reportedly used by Winner under the handle 'Sara Winners' has several tweets that express her frustration with the Trump administration and retweeted a joke about government leaks.

According to the FBI, 'Winner agreed to talk with agents during the execution of the warrant. During that conversation, Winner admitted intentionally identifying and printing the classified intelligence reporting at issue despite not having a 'need to know,' and with knowledge that the intelligence reporting was classified.'

Without a lawyer present, 'Winner further admitted removing the classified intelligence reporting from her office space, retaining it, and mailing it from Augusta, Georgia, to the news outlet, which she knew was not authorized to receive or possess the documents,' according to the government.

Winner's mother Billie Winner-Davis (pictured with husband Gary) said she was shocked to learn of her mother's arrest, but revealed she is 'very passionate about her views'

Donald Trump had vowed a crackdown on leaking confidential information to the media, and Winner is the first person to have been charged

According to the warrant, 'WINNER was an active duty member of the U.S. Air Force and held a Top Secret clearance.'

The Intercept story states that the documents raise the possibility that Russian-based hackers 'may have breached at least some elements of the voting system,' bringing the investigation of election interference to a new level.

Previous analyses by the intelligence community have stated that Russia was behind hacking into the Democratic National Committee and Hillary Clinton's campaign chair in an effort to impact the election, but have not provided evidence of a successful campaign to affect the vote count or voter rolls.

President Trump has repeatedly railed against leaks, and administration members have called on congressional committees to focus not just on alleged Russian interference, but 'unmasking' of individuals in leaked governments and leak investigations.

'It is my opinion that many of the leaks coming out of the White House are fabricated lies made up by the media,' Trump tweeted last week.