Facebook has consistently denied allegations that it listens to its users' conversations through their phone's microphone, but a new document suggests the tech giant has not ruled out doing so in the future.
Facebook users have been sharing circumstantial evidence for several years that suggests Facebook snoops on their private conversations in order to deliver more personalised ads. In April, US lawmakers finally brought the concerns to CEO Mark Zuckerberg in a hearing about data misuse on the firm's platform.
The social media firm released a 454-page document this week to follow up with questions posed to Mr Zuckerberg, after he was criticised for evading some of the most important ones.
During the testimony, Senator Ted Cruz asked if Facebook activates, monitors, or captures data from a microphone without a user's knowledge and consent.
Facebook responded: "No, Facebook does not engage in these practices or capture data from a microphone or camera without consent."
A follow up question asked Facebook to commit to "not using its platform to gather such audio or visual information surreptitiously." Facebook did not answer the question, instead saying: "See response to [previous] question."
The comments are unlikely to quell concerns that Facebook is spying on its users, with many convinced by experiments testing the premise.
One video from 2016, which has been viewed on YouTube more than 1.7 million times, claims to show how Facebook picked up on keywords in order to serve ads for cat food.
Rob Goldman, Facebook's vice-president of advertising, said last year that it was "just not true" that the tech giant was using people's microphones to eavesdrop on conversations.
"I run ads product at Facebook," Mr Goldman tweeted in response to a thread about people's stories on the matter. "We don't – and have never – used your microphone for ads."
The tweet appears to have since been deleted.