Facebook acquired WhatsApp in 2014 for about $22 billion, and now Acton's focus is on data protection and privacy, as he wrote last month after donating $50 million to launch the Signal foundation. At the time, he said: "We believe there is an opportunity to act in the public interest and make a meaningful contribution to society by building sustainable technology that respects users and does not rely on the commoditization of personal data."

As of 8:30 PM ET, Acton's public Facebook profile is still active.