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Major tech companies are set to deliver testimony for the first time in public on Capitol Hill as part of congressional investigators ongoing probe into Russian interference in the 2016 election.

Representatives from Facebook, Twitter and Google will all testify before the Senate Judiciary Committee about what they know about specific attempts by Russian trolls to disseminate disinformation, political ads purchased on their given sites and what efforts they are taking now to prevent further incidents of meddling from happening in future elections.

A source familiar with Facebook’s prepared testimony on Tuesday says the company will disclose that over the course of three years, approximately 29 million people were “delivered” or “served” content from pages related to the Internet Research Agency (IRA) – the Russian troll farm associated with the fake campaign ads, CBS News’ Nancy Cordes reports.

Thanks to sharing and engagement, however, up to 126 million people could have seen this content over the course of three years.

Facebook’s Chief Operating Officer Sheryl Sandberg said in an interview earlier this month that the social media site has an “enormous responsibility” to release all ads purchased by foreign entities on the site as it relates to Congress’ investigation.

“Things happened on our platform in this election that should not have happened, especially, very troubling, a foreign interference in a democratic election, we have a responsibility to do everything we can do to prevent this kind of abuse on this kind of platform,” said Sandberg.

Similarly, a source familiar with the testimony being offered by Twitter to Congress in the same hearing, says that the social media platform connected the 201 accounts they identified with congressional investigators to broader Russian election-focused activity on Twitter, including the full set of 2,752 accounts that we now believe are associated with the Internet Research Agency or IRA.

All 2,752 accounts have been suspended and Twitter is now “proactively giving committee investigators the handles of these accounts, and we have taken steps to block future registrations related to these accounts– and we have pledged to Congress that we will inform them as we uncover more related accounts” according to the source.

They also claim that election-related Tweets generated by Russian-linked, automated accounts constituted less than three quarters of a percent (0.74 percent) of the overall election-related Tweets on Twitter at the time.

The companies are set to testify on Wednesday before the House and Senate Intelligence Committees, as well.

Follow Senate testimony updates below: