Everson is the first Facebook exec to take live, in-person questions about the recent allegations that Cambridge Analytica had never deleted improperly obtained user data that it received from a Russian-American researcher in 2015.
The firm told Facebook that it had deleted the data, while reports published by The New York Times and the Guardian this weekend said it did not. Everson reiterated that Facebook is conducting a "deep audit" to "understand what happened."
In the wake of the revelations, media and users have criticized Facebook for being lax about securing user information and for its top executives' lack of leadership in publicly addressing the situation.
The company's chief security officer, Alex Stamos, previously posted a string of tweets about how the incident didn't constitute a "data breach" and then deleted them.
He is reportedly leaving the company due to disagreements with management about how the company deals with disinformation.
Everson said that the allegations were "an incredible violation of everything that we stand for."