UPDATE: Additional information from The Washington Post:
The woman had worked as a local investigator in the U.S. Secret Service office in the embassy since 2001, the people said. But she was fired in early August 2017 after State Department investigators surveilled her movements and were alarmed to find her meeting and communicating with agents of the Federal Security Service, better known as the FSB, the people said.
It is unclear whether her FSB conversations led to any damage to national security.
(...)
In her job, she served as a liaison between Russian law enforcement and the Secret Service, and former embassy staffers said she would have had access to information about agency investigations of financial fraud and cybercrimes. Secret Service investigators were the first to identify the Russian government as directing the 2014 hack into the White House’s unclassified email system.
(...)
The woman was described by former co-workers as a native of St. Petersburg, a wife and mother, and a mild-mannered investigator who kept to herself. Her State Department employee picture shows a trim woman with a pale complexion and straight brown hair.
“She was not a social butterfly,” said David Rubincam, an FBI agent who served as the FBI’s legal attache in the U.S. Embassy in Moscow and retired in 2013. “There were a lot of Russians you would meet in the cafeteria. She wasn’t one of them. Pretty much kept to herself. Did her work and went home.”
(...)
To protect sensitive information, the U.S. Embassy in Moscow has created a “hard line” in the building, which means there are separate floors of offices where foreign service nationals are unable to go. U.S. Marines guard the entrance to their floors to check badges. People with blue badges — American staffers — can enter. Those with yellow badges — foreign nationals — cannot.
Russian who worked at U.S. Embassy in Moscow was fired amid suspicions she was spying (WaPo)
The Guardian reports a woman who worked for the Secret Service at the U.S. Embassy in Moscow for years was dismissed quietly last summer under suspicion of being a spy.
The Russian national had been hired by the US Secret Service and is understood to have had access to the agency’s intranet and email systems, which gave her a potential window into highly confidential material including the schedules of the president and vice-president.
The woman had been working for the Secret Service for years before she came under suspicion in 2016 during a routine security sweep conducted by two investigators from the US Department of State’s Regional Security Office (RSO).
They established she was having regular and unauthorised meetings with members of the FSB, Russia’s principal security agency.
The Guardian has been told the RSO sounded the alarm in January 2017, but the Secret Service did not launch a full-scale inquiry of its own. Instead it decided to let her go quietly months later, possibly to contain any potential embarrassment.
An intelligence source told the Guardian the woman was dismissed last summer after the state department revoked her security clearance. The dismissal came shortly before a round of expulsions of US personnel demanded by the Kremlin after Washington imposed more sanctions on the country.
The order to remove more than 750 US personnel from its 1,200-strong diplomatic mission is understood to have provided cover for her removal.
(...)
Asked detailed questions about the investigation into the woman, and her dismissal, the Secret Service attempted to downplay the significance of her role. But it did not deny that she had been identified as a potential mole.
CNN:
A person familiar with this case says the woman in question was actually employed by the State Department, but did work for the Secret Service as part of her job at the embassy. All foreign nationals are technically employed by the State Department -- which vets and hires them -- and then the different agencies assign them work.
A source claimed “her frequent contacts with the FSB gave her away ... numerous unsanctioned meetings and communications”.
The Guardian has been told the state department’s resident agents in charge alerted the Secret Service in January 2017 and at least nine high-ranking Secret Service officials became aware of the findings.
At the time, separate CIA and FBI inquires were also under way, but it appears the Secret Service was expected to take the lead. It failed to do so, according to a source.
“She had access to the most damaging database, which is the US Secret Service official mail system,” the source said. “Part of her access was schedules of the president – current and past, vice-president and their spouses, including Hillary Clinton.”
She had plenty of time to gather intelligence without supervision, the source said. “Several employees interacted with her on a personal level by emailing her personally on a non-work account. This isn’t allowed.”
The Department of Homeland Security was apparently notified about the case but it is unclear how much detail was passed on to officials outside the agency. It is also unclear why the woman, a Russian national, was hired by the Secret Service in the first place or what kind of vetting took place.
The Guardian has been told that the potential breach was not reported to any of the congressional intelligence or oversight committees.
A source said: “A government committee needs to investigate the Secret Service for hiding this breach.”
Another option would be to include it in special counsel Robert Mueller’s investigation into suspected Russian collusion in the 2016 presidential election.
“The US Congress is focusing on Russian hackers when it is possible that all of the information they needed to get into the system came from the internal breach in the Secret Service,” the source said.
“Her activities of stealing and sharing information could shed more light on how the Russians were able to hack the 2016 presidential election office of the DNC [Democratic National Committee].”
Suspected Russian spy found working at US embassy in Moscow (The Guardian)
Suspected Russian spy caught working inside US embassy in Moscow (CNN)