In a Senate Intelligence Committee hearing today, executives from Facebook and Twitter attempted to convince lawmakers that they have successfully stepped up efforts to combat foreign influencers’ attempts to abuse their platforms in order to spread disinformation and sow discord amongst democratic institutions.

Facebook also fielded questions related to its oft criticized user data privacy practices, while Google invited scorn by declining to send a high-ranking representative from the company.

Sheryl Sandberg, Facebook COO, acknowledged in both written and oral testimony that her company was “too slow” spot Russia’s attempts to interfere with the 2016 U.S. elections “and too slow to act” to stop such activity. But since that time, the company has doubled the number of people working in its Safety and Security department to 20,000, while also investing in new tools and technologies such as artificial intelligence and third-party fact checkers.

Sandberg said Facebook disabled 1.27 billion fake accounts from October 2017 to March 2018, and in July removed 32 Facebook/Instagram pages and accounts due to “coordinated in authentic behavior” consistent with past activity by Russia’s Internet Research Agency, only more difficult to attribute.

“We’re shutting down fake accounts and reducing the spread of false news. We’ve put in place new ad transparency policies, ad content restrictions, and documentation requirements for political ad buyers. We’re getting better at anticipating risks and taking a broader view of our responsibilities. And we’re working closely with law enforcement and our industry peers to help find bad content and locate bad actors.”

Meanwhile, Twitter CEO Jack Dorsey testified that his company has “refined its detection systems,” prioritizing anomalous account behavior (such as high-volume posting) and increasing its use of challenges such as reCAPTCHAs to eliminate automated bot accounts.”Twitter is also in the process of implementing mandatory email or cell phone,” Dorsey said in written testimony.

Dorsey reported that as a result of its improvements, Twitter is “now removing 214 percent more accounts year-over-year for violating our platform manipulation policies.” And just the last few months, Twitter has challenged about 8.5-10 million accounts per week due to misuse or automation or spam distribution, he added. Moreover, “We thwart 530,000 suspicious logins a day, approximately double the amount of logins that we detected a year ago.”

In response to questioning, Dorsey also told Congress that Twitter has been “considering over the past few months” implementing a feature that would inform users when they are interacting with an autonomous bot, as opposed to another human being. “Where is gets tricker is that automation is actually scripting our website to look like a human actor,” he said.

Committee Chairman Sen. Richard Burr, R-N.C., applauded Facebook and Twitter’s recent announcement that they collectively removed hundreds of inauthentic pages and accounts linked to separate coordinated influence campaigns linked to Iran and Russia, respectively. However, “I’m not sure your success is the big story here. As I understand it, a third-party security team was crucial to identifying the scope of the Iranian activity,” said Burr, referring to FireEye as the third-party. “And even more concerning is that more foreign countries are now trying to use your products to shape and manipulate American as an instrument of statecraft.”

Committee Vice Chairman Mark Warner, D-Va., agreed that the threat is only growing more dangerous, as Russians get better at hiding their activity and other countries adopt their playbook. “I’m skeptical that ultimately you’ll be able to address this challenge on your own,” said Warner, who also expressed concern that DeepFake technology will soon cast doubt on the veracity of video content. “I believe that Congress is going to have to act,” he added.

Warner also expressed displeasure over Google’s failure to appear before the Senate, citing “structural vulnerabilities on a number of Google’s platforms, from Google search, which continues to have problems surfacing absurd conspiracies, to YouTube, where Russian-backed disinformation agents promoted hundreds of divisive videos, to Gmail, where state-sponsored operatives attempted countless hacking attempts.”