THE world’s largest social network has become embroiled in a tit-for-tat battle with former and current employees of Facebook over pushing privacy boundaries, breaking encryption in favour of advertising, and making big changes to WhatsApp and Instagram against the wishes of their creators.

The stoush, which followed the double resignation of Instagram founders earlier this week, fired up overnight when former WhatsApp creator Brian Acton gave his first public interview after his resignation, damning Facebook chief executive Mark Zuckerberg as an impersonal businessman set on making “a buck” over a useful product.

But a current Facebook employee slammed Mr Acton’s comments as “a whole new standard of low class,” criticising him for “attacking the people and company that made (him) a billionaire”.

Facebook blockchain head David Marcus launched his criticism in a blog post published on the social network; an unprecedented act he said “no one at Facebook asked” him to perform.

In his post, titled “The other side of the story,” Mr Marcus promoted Facebook as a company giving founders “unprecedented autonomy,” arguing that Mr Zuckerberg defended and shielded WhatsApp’s creators from outside pressure, and slamming Mr Acton for speaking out.

“Call me old fashioned,” he wrote, “but I find attacking the people and company that made you a billionaire, and went to an unprecedented extent to shield and accommodate you for years, low class. It’s actually a whole new standard of low class.”

Mr Acton resigned from Facebook last year, losing out on a $US850 million payday that would have been his if he stayed for an additional year. WhatsApp co-founder Jan Koum followed him in May.

As rumoured, Mr Acton said he quit over disagreements with Mr Zuckerberg and chief operating officer Sheryl Sandberg who proposed adding targeted advertisements in WhatsApp rather than charging users small amounts to keep the messaging app profitable.

“They are businesspeople, they are good businesspeople. They just represent a set of business practices, principles and ethics, and policies that I don’t necessarily agree with,” Mr Acton told Forbes.

“The CFO projections, the 10-year outlook — they wanted and needed the WhatsApp revenues to continue to show the growth to Wall Street.”

Mr Acton, who sold WhatsApp to Facebook in 2014 for $US22 billion, said his vision for WhatsApp as an ad-free encrypted messaging app was in direct contrast to views by the Facebook leadership team, and Ms Sandberg shot down his plan to charge users.

“I called her out one time. I was like, ‘No, you don’t mean that it won’t scale,” he said. “You mean it won’t make as much money as …’ and she kind of hemmed and hawed a little. And we moved on. I think I made my point.”

Mr Acton said he disagreed with Facebook’s fundamental approach to products — “if it made us a buck, we’d do it” — convincing him to resign.

Facebook also tried to get him to sign a nondisclosure agreement as part of a settlement, he said, and Mr Zuckerberg made it clear they were not parting on good terms: “He was like, ‘This is probably the last time you’ll ever talk to me’.”

Since leaving the company, Mr Acton also let an investment do the talking, sinking $50 million into a rival messaging app called Signal.

The latest war of words follows the Facebook departure of both Instagram founders, Mark Krieger and Kevin Systrom this week, who reportedly disagreed with Mr Zuckerberg over plans to feed more users from the photo-sharing network to Facebook, and over their dwindling autonomy.