Former Cambridge Analytica data analyst Christopher Wylie said during Sunday's episode of NBC's Meet the Press that the number of Facebook users "could be higher" than the 87 million users already acknowledged by the social network.
"There is a genuine risk that this data has been accessed by quite a few people," Wylie said on the program, "and that it could be stored in various parts of the world, including Russia, given the fact that the professor who was managing the data harvesting process was going back and forth between the UK and to Russia."
Wylie was referring to a Cambridge lecturer named Aleksandr Kogan, who collected the data legitimately through a personality quiz app but then violated Facebook's terms by sharing the information with Cambridge Analytica, a firm later hired by the Trump presidential campaign during the 2016 US election.
Facebook learned of the infraction in 2015 but didn't inform the public. Instead, the company demanded that all the parties involved destroy the information. But now there are reports that not all the data was deleted.
The data could have been copied several times after it left Facebook's database, Wylie said when he was asked whether Facebook could determine how many people had access to the information.
"I know that Facebook is now starting to take steps to rectify that and start to find out who had access to it and where it could have gone, but ultimately it's not watertight to say that we can ensure that all the data is gone forever," he said.
Facebook reiterated on Sunday that the 87 million figure is the social network's estimate of the maximum number of users whose data could have been transferred to Cambridge Analytica.
Cambridge Analytica, for its part, has said through a series of statements that the allegations against it are incorrect and that it acted appropriately.
Facebook CEO Mark Zuckerberg has repeatedly for his company's involvement in the scandal in TV interviews as well as newspaper ads and agreed to on Tuesday to answer questions about how his company uses and protects the data of its more than 2 billion users.
But Zuckerberg has reportedlyto appear in person to answer similar questions to the UK's Parliament -- a stance Wylie criticized in his interview.
"Why is it that Mark Zuckerberg won't actually bother to come and attend a Parliamentary inquiry here in the UK, as everyone else is?" he said.
iHate: CNET looks at how intolerance is taking over the internet.
Life, Disrupted: In Europe, millions of refugees are still searching for a safe place to settle. Tech should be part of the solution. But is it?