WhatsApp co-founder Jan Koum has put out word that he is leaving Facebook, which bought the smartphone messaging service four years ago for $19 billion.

Koum said in a post on his Facebook page that he is taking time off to pursue interests such as collecting air-cooled Porsches, working on cars and playing ultimate Frisbee.

US media reports indicated that a disagreement with Facebook over the privacy of user data may have also been a factor in Koum’s decision to quit his position as a high-ranking executive and likely leave his seat on the board at the leading online social network.

“It’s been almost a decade since Brian (Acton) and I started WhatsApp, and it’s been an amazing journey with some of the best people,” Koum said in the post.

“But it is time for me to move on.”

Acton left Facebook last year to start a nonprofit.

WhatsApp boasts more than 1.2 billion users worldwide.

In a reply to Koum’s post, Facebook co-founder and Chief Executive Mark Zuckerberg said he would miss working closely with the WhatsApp co-founder.

“I’m grateful for everything you’ve done to help connect the world, and for everything you’ve taught me, including about encryption and its ability to take power from centralised systems and put it back in people’s hands,” Zuckerberg said in his written reply.

“Those values will always be at the heart of WhatsApp.”

WhatsApp last week raised its minimum age for users in the European Union to 16 years, as the bloc prepares for a new online privacy law to come into force next month.

In an update to its terms of service, WhatsApp said the minimum age for users outside the EU was still 13 years.

WhatsApp parent Facebook has pledged to change how it handles private data to comply with the forthcoming law change.

But unlike WhatsApp, which will only apply the new law to its European users, Facebook plans on rolling out changes for its users worldwide.

The change in the European law was already planned prior to the recent privacy scandal involving Facebook and Cambridge Analytica.

Zuckerberg has spent most of the past month on the fallout from revelations on the hijacking of personal data by the political firm, seeking to assuage fears that the California-based internet colossus can safeguard privacy while making money by targeting ads based on what people share about themselves.