A new feature on the popular online social network Facebook is causing a backlash from its users, who say it invades their privacy.

Facebook announced the feature, called News Feed, this week. It's an automated system that alerts users to changes in the profiles of their friends and classmates.

A Facebook user who logs in to the site could immediately see if someone on his friends list has joined a new group, posted new photos or announced that they're single again.

Users of the service said the alert system invaded their privacy and formed a group within Facebook called "Students Against Facebook News Feed." It had over 700,000 members on Friday.

Facebook is a online networking service for college and university students with over 7.5 million users.

The founder and CEO of Facebook, Mark Zuckerberg, responded to the controversy on his blog Wednesday.

"The privacy rules haven't changed. None of your information is visible to anyone who couldn't see it before the changes," he wrote.

On Friday, Zuckerberg apologized for the controversy over the News Feed features.

"We really messed this one up," he wrote.

"When we launched News Feed … we were trying to provide you with a stream of information about your social world. Instead, we did a bad job of explaining what the new features were and an even worse job of giving you control of them," wrote Zuckerberg.

He said the Facebook programmers were working on implementing better privacy controls on the News Feed feature.