Facebook fears that the confidential internal documents published by Parliament earlier this week may only be a fraction of what has been leaked.
Lawyers for the social media giant told a California judge on Friday that they still did not know what other material might now be in circulation and might soon be released.
The emails and memos, seized last month by MPs from an American app developer, Ted Kramer, and published on Wednesday, are part of a legal archive thought to include hundreds of thousands of documents.
"We literally don't know what information is out there," said Sonal Mehta, counsel for Facebook in court on Friday. "We have 250 pages that we know are public because they were published this week... but Mr Kramer can't tell us what else is out there or who else might have it.”
The documents were gathered as part of an ongoing lawsuit against Facebook by Mr Kramer's defunct app company, Six4Three, and had been sealed from the public by order of the judge.
Among them were emails showing that Facebook tried to strangle its competitors by cutting off their access to its data, as well as emails in which Facebook employees discussed how to read users' mobile phone logs without prompting a dialogue box asking for their consent.
In Redwood City, California on Friday, Facebook's lawyers sought to control the extent of the leaks and skirmished with Six4Three's legal team over how exactly the secret emails found their way into the hands of British MPs.
Mr Kramer says that he "panicked" into handing over the documents in during a visit to the UK when Damian Collins, head of the House of Commons committee investigating Facebook, threatened him with jail for the obscure and rarely-used offence of "contempt of Parliament".
But Facebook accuses Mr Kramer and his associates of deliberately leaking the documents as part of a "longstanding plan" to circumvent the court order and "leak information to the press for their own ulterior motives".
Last week the company's lawyers convinced Judge V. Raymond Swope of the Superior Court of California to seize Mr Kramer's laptop, his mobile phones and his cloud storage accounts for forensic analysis to find out just which documents he had transferred.
Ms Mehta said on Friday that there was strong evidence that Mr Kramer had been "plotting" for around two years to leak the information and that he had pointedly invited Mr Collins to take the information from him by saying that he could not "voluntarily" disclose it.
Jack Russo, counsel for Mr Kramer, denied the allegations, saying that "there was no plan" to leak documents and that Mr Kramer was "subject to circumstances that took him completely by surprise".
"There's a suggestion that Mr Kramer has superpowers over Parliament," Mr Russo told the court. "I think that's crazy. That Mr Kramer somehow caused a subpoena to be served on himself, and then to be threatened with incarceration, that he actually induced and wanted that, I think it's absurd on its face."
Prompted by a skeptical Judge Swope as to why Mr Kramer had journalists that he was in possession of confidential documents, Mr Russo said only that "sometimes people decide to tweak the press to get their interest".
Ms Russo also questioned Facebook's motives, asking: "What is the endgame here? Is it to punish Mr Kramer for an inadvertent mistake, or a negligent mistake? Or is it some broader purpose?"
When asked how Mr Collins had known Mr Kramer was in the UK, Mr Russo appeared to blame Carole Cadwalladr, a journalist for the Guardian, who Mr Kramer has previously said was the only person who knew where he was staying.
He suggested Ms Cadwalladr might have to testify to the California court about why and how Mr Kramer came to hand over the documents.
Six4Three, the maker of an app called Pikini which allowed users to find photographs of their friends in bathing suits, contends that Facebook unfairly cut off access to its data in 2015 while allowing other companies to keep using it.
Facebook admits that some companies retained access to the data long after the changes, but said it had every right to stop "sketchy" apps from using its platform and that the case is "baseless".
The court later heard from Thomas Scaramellino, reportedly an investor in Six4Three who worked as "legal intern" on its side of the case and who is seeking to qualify as a lawyer in California.
Facebook had accused Mr Scaramellino of setting up the Dropbox account that allowed Mr Kramer to access the documents, which should have been restricted to Six4Three's legal team.
"This is a simple lawsuit," said Judge Swope. "At least, it started out that way... confidential information should have been confined to this lawsuit. There should not have been any conversations with third parties."
Mr Scaramellino admitted that he had spoken with third parties about the case but hotly contested any suggestion he had done so as prat of a "conspiracy" to disclose confidential information
"Our position is that this is in the public interest," he said. "Facebook has committed corporate fraud on a massive scale and it must be investigated by regulators. That was our motive for communicating about the lawsuit."
"You don't talk over a judge," Judge Swope upbraided him at one point. "That's something you'll learn when you're admitted to the bar. It's not well-received."
Mr Scaramellino was ordered to hand over his laptop and email passwords to forensic investigators.