US senators have attacked social networking site Facebook over its action of sharing users' personal information with third-party websites without the explicit approval of the users.

Senators Charles Schumer and other called on Facebook to stop immediately sharing users’ information with other sites. They also asked it to rationalize its complex privacy settings.

They said that Facebook should ask users to "opt into" the feature rather than "opt out".

They wrote a letter to Facebook founder Mark Zuckerberg, saying, "The innovation they represent is welcome but users need to have the ability to control their private information and fully understand how it's being used."

The comments emerged after Facebook started sharing users’ personal information with three other websites viz. music site Pandora, review site Yelp and Microsoft's document site Docs.com.

Meanwhile, the Electronic Privacy Information Center, a privacy watchdog group, said that it drag Facebook to the Federal Trade Commission over privacy issue.