MANILA, Philippines - A @facebook.com email? The social networking site thinks its a good idea - but users are furious.

Over the weekend, Facebook, without warning, changed all of its users' public email addresses with @facebook.com ones, leaving millions of users puzzled and many angry at what they see as another infringement in their privacy.

Facebook's email service isn't new - it has been in place since 2010, and was first thought as the "Gmail Killer" since it is integrated into the world's top social network. However, it failed to get traction among its 900 million users.

On Monday, June 25, Forbes magazine said the email address change was first noticed by some users around Saturday, June 23. Users suddenly have a @facebook.com email address, instead of the ones they formerly used as their public email address on their profiles.

The old email addresses are still there, but were automatically hidden by the social network, without any notification for the user.

This earned the ire of many users. User Gervase Markham, a programmer, said the social networking site "silently inserted themselves into the path of formerly-direct unencrypted communications."

"In other contexts, this is known as a Man In The Middle (MITM) attack," Markham, one of the first to notice the change, said.

Forbes, meanwhile, said the move was a "lame attempt to force its email service" on users. It quoted security researcher Ashkan Soltani, who said it is "slightly fishy to auto-replace your default email address with 'facebook.com' without any user consent."

"This is another in a long line of ‘nudges’ Facebook gives users to try to get them to spend more time on the site, and to make it users’ sole destination when they go online," Forbes added.

The company, meanwhile, said they have been updating Facebook addresses for users since April.

In an email to Reuters' Matthew Keys, Facebook said that they have been updating addresses "to make them consistent across [the] site."

"In addition to everyone receiving an address, we're also rolling out a new setting that gives people the choice to decide which addresses they want to show on their timelines," the company said.

"We basically defaulted to show your Facebook address as we rolled this out, just to keep it consistent for everyone," Meredith Chin, manager of product communications for Facebook, told CNNMoney.com. The site added the company "seemed surprised" by the reaction.

However, she could not explain why Facebook did not warn users of the change.

Jerk move

Despite this explanation, many users are not satisfied with the forced change.

"They did not explain why (or even acknowledge) that all of these addresses were made default on people's profiles," LifeHacker.com said.

"It was a big jerk move for Facebook to do this without asking permission, or even telling you that it happened," the site said.

Many tech sites are now giving instructions to users revert back to their old address. LifeHacker summed it up through these steps:

• Click "About" on your profile and scroll down to your email address. Click "Edit" to change them.
• Click on the circle next to your Facebook email address and change its setting to "Hidden From Timeline".
• Click on the circle next to your other email addresses and change their settings to "Shown On Timeline".
• Click the Save button at the bottom of the Edit popup.

The forced email change is being rolled out to all Facebook users, Chin told CNNMoney.com. - Rappler.com