The date of his departure isn't known.
However, their relationship with Facebook has soured recently, according to reports.
Koum's post was curiously clear of any reference to Facebook: "It's been nearly a decade since Brian and I started WhatsApp, and it's been an awesome journey with some of the best people". It doubled down on its pledge by adding encryption in 2016. Facebook has been under the cosh for allegedly, not using that information in an ethical manner.
Facebook, though, needs to prove that its investment in WhatsApp - its largest acquisition ever - was worth it.
Jan Koum's exit from Facebook could prove costly. The inner circle of management - and the Board of Directors - have been fiercely loyal during the scandals that have rocked the social media giant.
Executives posting their resignations on Facebook. Acton quit the company a year ago to start his own non-profit. He has joined a chorus of former executives critical of Facebook. "I've been blessed to work with such an incredibly small team and see how a insane amount of focus can produce an app used by so many people all over the world", Koum wrote in his post. That encryption is what allows messages sent on the app to only be accessible to the sender and receiver.
Acton left WhatsApp in September 2017, and now Koum is following suit. It caught the attention of Zuckerberg, who was looking to expand the social network overseas. Given that WhatsApp also doesn't run any advertising, the unit remains a strangely un-monetised arm of Facebook's empire. With both of the founders gone from the company, it is unknown what shape WhatsApp would take in the coming future. They said that online advertising was "a disruption to aesthetics, an insult to your intelligence, and the interruption of your train of thought".
However, encryption also prevents Facebook from using technology to scan messages for the goal of injecting targeted advertising at users - similar to the way in which Google scans messages in Gmail for the objective of advertising.
According to reports, Koum had informed the Facebook bosses about his intentions of leaving the company in the past.
- WhatsApp finally goes completely free as Koum announced in January that WhatsApp will no longer charge its users a $1 annual subscription fee. "And you can still count on absolutely no ads interrupting your communication".
Facebook's COO Sheryl Sandberg also commented, "Jan, the work you've done building WhatsApp has connected so many people around the world". However, Facebook in particular is being vilified for an alleged lack of care over how users' data is utilized or its platform is manipulated. The protocol is well-tested and well-regarded open source code that makes content transmitted on WhatsApp unintelligible to everyone but the intended recipients, using what's referred to as end-to-end encryption.
Even with the threat that Facebook would eventually start to use data from WhatsApp users, the messaging service continued to grow.
Moreover, the two also clashed over the introduction of a mobile payments system (still in trial phase) on WhatsApp in India.
- Following security threats in August, WhatsApp announced that messages will be encrypted in the "latest version" of WhatsApp for iOS and Android. It was stated this was done to increase WhatsApp's users and allow businesses to chat with customers.
In particular, the executive said, Mr. Koum was exhausted from fighting back against pressure from the board throughout 2017 to allow advertisements on WhatsApp.
As for Koum's co-founder, after the Cambridge Analytica story - in which the political data consulting firm accessed the accounts of up to 87 million Facebook users without their permission - became a big, fat headache for Facebook in March, Acton was among those who called on people to delete their Facebook accounts.