In the two years since Facebook’s social media platform was leveraged by Russian intelligence agencies seeking to sway the 2016 presidential election, founder Mark Zuckerberg says he has systematically devoted staff and technology to blocking further exploitation.

“We’ve fundamentally altered our DNA to focus more on preventing harm in all our services,” he said in a letter to Facebook’s 2 billion monthly users that recapped the Menlo Park, Calif.-based company’s response to U.S. lawmakers’ concerns about handling of consumer data, hate speech and election interference.