U.S. news reports say Facebook founder Mark Zuckerberg is expected by Thursday to speak to the public about the social network's response to allegations of illegal data collection. Zuckerberg has remained silent since Facebook disclosed on Friday that it knew a data collection company had collected Facebook user data without users' consent. Meanwhile, Facebook's stock value has taken a significant hit. Lawmakers and Facebook users are asking why Facebook did not inform the public sooner that the research firm Cambridge Analytica had taken their information illegally from a psychology researcher who collected the information legally through a personality quiz. The data was supposed to be destroyed after the British researcher, Aleksandr Kogan, used it for his work. Instead, Cambridge Analytica obtained and kept the personal information of 50 million Facebook users without their permission. The data was used to build voter profiles for U.S. political campaigns. Facebook said in a statement Tuesday that Zuckerberg and Chief Operating Officer Sheryl Sandberg had been "working around the clock" to get all the facts of the issue and "take appropriate action." The statement acknowledged that the problem is serious, adding, "The entire company is outraged we were deceived." Questions about regulation Among the tough questions the company faces: Why it did not inform the affected users about the issue. On Monday, the firm's stock dropped nearly seven percent, losing $36 billion in value, Facebook's biggest one-day decline in nearly four years. In early trading Tuesday, Facebook shares were down about 3 percent. The probe over Cambridge Analytica is just the latest flashpoint around Facebook's role in the 2016 election and comes as the company faces questions about how it should be regulated and monitored going forward. With its more than 2 billion monthly users and billions of dollars in profit, Facebook has become a powerful conduit of news, opinion and propaganda, much of it targeted at individuals based on their own data. The social media site and investigators have found that Russia-backed operatives had used Facebook to spread disinformation and propaganda. In recent months, the company, along with YouTube and Twitter, has changed some of its practices to reduce the power of automated accounts and propaganda. Facebook has said it would hire 10,000 security employees. Data-mining company Facebook's most recent troubles began in 2013 when an app called "Thisisyourdigitallife" developed by Kogan, a Cambridge University professor, offered users a personality survey. The users were invited to download the app, which then gathered user information about their profiles and that of some of their friends. The professor shared data with Cambridge Analytica, the data-mining firm that worked with President Donald Trump's campaign, according to The New York Times and The Observer. While the gathering of the data was legitimate at the time, Facebook says the professor did not abide by the company's rules when he passed the data to a third party — Cambridge Analytica — thus violating Facebook's terms and conditions. Facebook discovered the violation in 2015 and required Cambridge Analytica to delete the data, but didn't tell affected users. Cambridge Analytica has denied that it kept the data. One Facebook executive in charge of security is reportedly leaving the firm as a result the matter.