WOODBURY - Facebook stirred controversy Monday after admitting to conducting a study without letting users know.

The social media site looked at the network's emotional impact with a weeklong study that happened more than two years ago.

Facebook says it manipulated the feeds of nearly 700,000 users. Researchers used key words to see whether or not positive or negative comments appeared on users' feeds. Researchers say users gave permission when they agreed to the site's data policy when opening a Facebook account.

Privacy and Technology Attorney Jonathan Ezor says the problem is that people didn't realize the study was happening. "In psychology studies, there are usually issues of ethics and consent. And on the Internet, there are issues of consent. Facebook seemed to not be concerned about either side," he said.

One of the study's co-authors apologized on his page. He said he thought the study would show that people may avoid Facebook if comments were consistently negative.

Either way, social media experts say the point of most social networking sites is exactly this -- to learn details about you and sell it.

Facebook isn't saying it sold any of this information, but privacy experts say it is an important reminder that any time you sign up for something online, you have to consider what information you may be sharing and what freedom you may be giving up in the process.