Mark Zuckerberg had told Congress in April that it ended this policy of massive data sharing in May 2015. But in its 748-page response to questions from the House Energy and Commerce Committee, the company admitted that it had granted a handful of companies permission to continue to have access to that data for six extra months. Mail.ru was on the list of companies granted this favor.

While Americans have been justifiably appalled that an obscure political consulting firm, Cambridge Analytica, had rich behavioral data on at least 87 million voters, we should be more concerned that companies like Mail.ru had access to the same data.

The Russian company was founded by Yuri Milner, a businessman who was a major investor in Facebook. Mr. Milner sold his shares in Facebook in 2013 and left Mail.ru years earlier. The Paradise Papers, a collection of secret documents showing how the wealthy hide their money, showed that Mr. Milner had received hundreds of millions of dollars from the Russian government, which he invested in Facebook and Twitter. He has also invested in a real-estate investment company run by Jared Kushner.

Facebook has not released the full list of thousands of companies around the world that had similar, almost complete, access to our likes and desires for years. The public might never know how many of these companies were connected to other dangerous and destructive forces in the world.