In brief: Signal founder Moxie Marlinspike has stepped down as CEO of the encrypted instant messaging service. He's still hunting for a permanent replacement but in the meantime, WhatsApp co-founder Brian Acton will serve as the company's interim chief.

Marlinspike said his goal has always been for Signal to grow and sustain beyond his involvement but until recently, that simply wasn't possible. Just four years ago, he was still the one writing all of the Android and server code for the service and was the only person on call. He was also doing all of the product development and even had to keep his laptop handy at all times in the event of a service disruption.

Things are far different nowadays. Signal currently has 30 employees comprised of engineers, designers, support staff and a leadership team. Marlinspike rarely writes code now and no one person is ever perpetually on call, he said.

Given the company's current standing, Marlinspike said he now feels comfortable replacing himself as CEO.

The search for a new leader has been going on for a few months but Marlinspike wanted to expand it with this week's announcement to help find the best person for the job.

In the interim, Signal Foundation board member Brian Acton has volunteered to serve as interim CEO until a permanent replacement can be found. Acton co-founded WhatsApp several years back and also spent time at Yahoo, Apple and Adobe Systems before that.

Marlinspike will remain on the Signal board and will transition out of the CEO role to help with the search for a permanent replacement.