Facebook Inc. Chief Executive Mark Zuckerberg on Wednesday said he believed secure private messaging would become more popular than open platforms, the latest sign that one of the companies that popularized social networking sees its future in more intimate online conversations.

Facebook (FB) already is one of the biggest global players in private messaging with its Messenger and WhatsApp, but faces a business challenge because encrypted conversations limit the company's ability to send targeted advertisements.

The company has faced criticism about its ability to safeguard users' privacy in hearings in the U.S. Congress and elsewhere.

"As I think about the future of the internet, I believe a privacy-focused communications platform will become even more important than today's open platforms," Zuckerberg wrote in a post on his Facebook page.

Zuckerberg said Facebook would focus more on the privacy of users as the social media network shifts its messenger products to end-to-end encryption, stopping any outsiders, including Facebook, from monitoring the conversations.