Facebook secretly experiments with users' News Feeds

[NOISE] A secret experiment carried out by Facebook ia causing an uproar among its users. The Facebook feeds of nearly 700000 users, were filtered to feature more positive or negative content. Based on certain key words like excited, they can either make them more positive or more negative. And what they found is that the way that people talk on Facebook tends to impact the way that users feel. The study, which was published recently, took place over the course of a week in January 2012. It was conducted by two universities and Facebook's data sciences team. They need to make sure that they understand their user base. So, that they can serve us more appropriate adds, which is they way that they make money and keep running. Participants where never notify, and that's anger many. Facebook is about me and my friends. It's not suppose to be about manipulating in some way. But every user essentially grants the social network permission to conduct this kinds of experiments. When they create their accounts. There really isn't much recourse other than going to Facebook and deleting your account. In a statement, Facebook told c/net that it does research to quote: make the content people see on Facebook as relevant and engaging as possible. A big part of this is understanding how people respond to different types of content, whether it's positive, or negative in tone. Facebook also says it has a strong, internal review process. But, that may do little, to ease users' concerns, over, future testing. In San Fransisco, I'm Sumi Das, CNET.com for CBS News. [MUSIC]