Jan Koum, who co-founded messaging service WhatsApp in 2009, said on Tuesday he was leaving the Facebook-owned company. He will quit because of clashes with Facebook over data privacy concerns, unidentified officials told The Washington Post.

Another co-founder, Brian Acton, had resigned from the company in November. In March, Acton joined the #DeleteFacebook chorus in the wake of a data breach scandal.

Acton and Koum always maintained privacy and encryption of users’ chat history as a key tenet of their service, and sold their company to Facebook in 2014 on the condition that this principle would not be diluted.

The company has more than 1 billion daily users.

Koum quit amid disagreements over Facebook’s attempts to use WhatsApp’s personal data and weaken its encryption, officials told The Washington Post. Soon after the newspaper’s report, Koum announced his departure in a Facebook post, without giving any reasons. He did not comment on the report.

“It’s been almost a decade since Brian and I started WhatsApp, and it’s been an amazing journey with some of the best people,” Koum said in his post. “But it is time for me to move on.”

He did not give a date for his exit. “I’m leaving at a time when people are using WhatsApp in more ways than I could have imagined,” Koum wrote. “The team is stronger than ever and it’ll continue to do amazing things. I’m taking some time off to do things I enjoy outside of technology, such as collecting rare air-cooled Porsches, working on my cars and playing ultimate frisbee. And I’ll still be cheering WhatsApp on – just from the outside.”

Facebook Chief Executive Officer Mark Zuckerberg commented on Koum’s post, saying he was grateful for what Koum taught him about encryption “and its ability to take power from centralised systems and put it back in people’s hands”. “Those values will always be at the heart of WhatsApp,” Zuckerberg wrote.