Investing.com - When Facebook (NASDAQ:FB) CEO Mark Zuckerberg testifies before Congress this week, he may need to convince investors as much as legislators that his company can be trusted to protect user data.Facebook shares are just beginning to show signs of recovering from their 18% swoon since the data privacy scandal emerged in mid March.Zuckerberg has made an extra effort to address the scandal, a smart strategy after it became known that the Cambridge Analytics data leak involved 87 million users not the originally disclosed 50 million. Zuckerberg said he takes personal responsibility for the episode and that the company will undertake a three-year effort to prevent it from happening again.Equally importantly perhaps, he also said the scandal has had no "meaningful impact" on the behavior of users and advertisers.That message may have been meant for Wall Street, where several firms had lowered their stock price targets as a result of the scandal. One firm, Deutsche Bank (DE:DBKGn), quickly concluded that Zuckerberg's comments suggest "the worst is likely behind" Facebook.Zuckerbe rg will need to drive that point home in his appearance on Capitol Hill.