A Facebook engineer warned in 2014 about a potentially huge data issue involving Russia, according to a UK lawmaker who reviewed a cache of sealed Facebook documents.

The engineer is said to have warned that "entities with Russian IP addresses had been using a Pinterest API key to pull over 3 billion data points a day."

During a hearing on Tuesday, the UK lawmaker, Damian Collins, asked Facebook's policy chief, Richard Allan, whether the potential data breach was reported. Allan did not answer.

Following the hearing, Facebook said it investigated the issue and "found no evidence of specific Russian activity."

A Facebook engineer warned in 2014 about a potentially huge data issue involving Russia, according to secret documents seized by Britain's Parliament last week.

Damian Collins, a UK politician, has reviewed the papers, which stem from a protracted legal battle between Facebook and an app developer named Six4Three.

Collins disclosed the potential breach at an international grand committee hearing on Tuesday in which Facebook was grilled on its series of scandals.

Summarizing an element of the documents, Collins said that "an engineer at Facebook notified the company in October 2014 that entities with Russian IP addresses had been using a Pinterest API key to pull over 3 billion data points a day through the Ordered Friends API."

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He asked Facebook's policy chief, Richard Allan, who was giving evidence in Mark Zuckerberg's place after the CEO refused to show up, whether the matter was reported to an external body at the time.

"Was that reported, or was that just kept — as so often seems to be the case — was that just kept in the family and not talked about?" Collins said.

Allan did not answer the question and said the information in the documents in Collins' possession was "at best partial, at worst misleading."

Collins said the data issue was raised in an email from a Facebook engineer. He asked Allan to report back to the committee with more information on the matter.

Following the hearing, Facebook said it investigated the issue. "The engineers who had flagged these initial concerns subsequently looked into this further and found no evidence of specific Russian activity," a spokeswoman said.

Facebook is still dealing with the fallout from the Cambridge Analytica scandal, in which the information of up to 87 million users was compromised.

The secret Facebook documents will remain secret — for now

Collins secured the Facebook documents from Ted Kramer, the founder of the software company Six4Three, who obtained them as part of legal action his firm is taking against Facebook in California. Six4Three claims that its Pikinis app was killed when Facebook stopped app developers from accessing Facebook friend data in 2015.

Kramer was compelled to hand over the documents on a recent visit to London. After initially refusing, he was escorted to Parliament, where he was told he could face a fine or imprisonment if he failed to produce them.

The documents are under seal by court order in California. Collins could publish them using UK parliamentary privilege, but he said on Tuesday that he would not do so for now.