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Facebook was hit on Tuesday by a well-meaning intruder who took over some of the site's online groups as a way of sending a message: "Think about the safety in your social media life to the same extent you do in your real life."

The social networking site, with more than 300 million users worldwide, has thousands of different groups that members can join, from college alumni to those who support various causes. It's not clear how many of the groups were taken over by an organization calling itself "Control Your Info," but it may have been in the hundreds.

"There has been no hacking and there is no confidential information at risk," a Facebook spokesperson said in a statement. "We are still investigating this situation, but an extremely small number of groups have been affected."