Facebook senior staff brief Congress amid backlash over how users' data was used

Washington, DC -- On the heels of a rare series of public interviews by Facebook CEO Mark Zuckerberg - the social media giant is sending senior staff to Capitol Hill on Thursday to brief aides to key committees on the controversy over its role in the exposure of as many as 50 million of its users' private information to a data-science firm linked to the Trump campaign.

Members want additional detail on why Facebook permitted a Russian-American professor to collect data on more than 200,000 of its users, with consent, and then how that then mushroomed into up to 50 million users having their private information end up in the hands of a data mining firm, Cambridge Analytica. The data firm was financially backed in part by conservative mega-donor Robert Mercer.

Former Trump adviser Steve Bannon served as vice president up until he stepped down in 2016 to join the Trump campaign.

Senators also are demanding to know when and if that data was destroyed - as Cambridge Analytica certified to Facebook. The social media company is investigating whether that information was indeed deleted.

Facebook says it became aware of the potential unauthorized use of data in 2015.

ABC News has learned that Facebook deputy general counsel Chris Sonderby and deputy privacy officer Rob Sherman are expected to sit down with staff of the House Judiciary Committee and both the Senate Commerce and Judiciary Committees as bipartisan demand grows for Zuckerberg, COO Sheryl Sandberg, as well as, Chief Product Officer Chris Cox to testify in public.

One congressional aide said Thursday's briefings are a precursor to formal testimony from the senior executives.

A Facebook official said that - as of Thursday morning - no formal testimony before Congress has yet been requested.

"We have a responsibility to protect your data, and if we can't then we don't deserve to serve you," Zuckerberg announced in an online statement Wednesday, his first since the controversy erupted late last week. "I've been working to understand exactly what happened and how to make sure this doesn't happen again."

Zuckerberg announced that his company would make changes to the way it shares data with third-party apps.

But while the billionaire CEO apologized for the "breach of trust" in a CNN interview Wednesday evening, some members of Congress were angered by his noncommittal answer on testifying. Democratic Sen. Ed Markey on Facebook wrote: "You need to come to Congress and testify to this under oath."

Zuckerberg said he would gladly oblige if required.

"What we try to do is send the person at Facebook who will have the most knowledge about what Congress is trying to learn. So if that's me, then I am happy to go," Zuckerberg said.

Cambridge Analytica, for its part, tweeted Thursday, "We're committed to being responsible, fair and secure with data. We'll be working with everyone - Facebook, independent auditors, and the ICO - as their investigations continue."

Members of Congress on multiple committees have also called for Cambridge executives to testify.