An attack on Facebook’s (NASDAQ: FB) computer network has exposed the personal information of nearly 50 million users. The breach is the largest in the company’s history. News of the breach spread quickly across Twitter and other online sites.

While the investigation into the breach is still in its beginning stages, some details have been released. According to reports, the attackers gained access to user accounts by exploiting several flaws in Facebook’s code. Out of the three software flaws used to gain access to Facebook’s systems, two were introduced by the site’s “View As” feature, which was built to give users more control over their privacy.

Those two flaws were compounded by another flaw found in Facebook’s video-uploading program for birthday celebrations. The combination provided the hackers with the digital keys needed to access the accounts. Facebook said it had fixed the vulnerabilities and notified law enforcement officials. Company officials say they have not yet uncovered the identity or the origin of the attackers. The company has been unable to determine the extent of the attackers’ access to third-party accounts.

Facebook was already facing scrutiny over how it handles the private information of its users. Facebook users were targeted in a Russian misinformation campaign just prior to the 2016 Presidential Election. Months later, the company disclosed that British analytics firm Cambridge Analytica had improperly accessed the private information of 87 million Facebook users. Rohit Chopra, a commissioner of the Federal Trade Commission, stated, “Breaches don’t just violate our privacy. They create enormous risks for our economy and national security.”

Facebook has spent months setting up new systems to guard against attacks on its network in preparation for the midterm elections. The company has already disclosed its efforts to deal with a number of incidents assumed connected to elections in Mexico, Brazil, and a few other countries.

That has not stopped some lawmakers from suggesting that the government will take action if Facebook does not get tighter control of its social network. Senator Mark Warner, (D-VA) said of this most recent breach, “This is another sobering indicator that Congress needs to step up and take action to protect the privacy and security of social media users.”