The head of popular messaging service WhatsApp is planning to leave the company because of a reported disagreement over how parent company Facebook is using customers’ personal data. WhatsApp billionaire chief executive Jan Koum wrote in a Facebook post Monday, “It’s been almost a decade since (co-founder) Brian (Acton) and I started WhatsApp, and it’s been an amazing journey with some of the best people. But it is time for me to move on,” he said. Koum did not give a date for his departure. The Washington Post reported Monday that Koum is stepping down because of disagreements over Facebook’s attempts to use the personal data of WhatsApp customers, as well as efforts to weaken the app’s encryption. Action left the company last fall and since then has become a vocal critic of Facebook, recently endorsing a #DeleteFacebook social media campaign. The Post, citing people familiar with internal WhatsApp discussions, said Koum …