One of the main critiques of the early social networking site, MySpace, was that it exposed personal information that employers and strangers could use against a person. Facebook was supposed to fix this by putting private information behind a wall that only friends could see, but in practice social networks tend to reveal a fair amount of what is posted.

While it turns out that not that many employers actually use social network data during hiring decisions, what people post does make a difference among those employers who do check. Discrimination is common.

That’s the finding of a new survey conducted by researchers at Carnegie Mellon. It recently completed a large-scale field experiment that looked into the effects of sharing personal information online via social networks.

"While it appears that a relatively small portion of U.S. employers regularly searches for candidates online, we found robust evidence of discrimination among certain types of employers," said Christina Fong, one of the researchers and a senior research scientist at CMU's Dietrich College of Humanities and Social Sciences.

While employers are not legally able to discriminate based on sexual orientation or religion, the study found that social networks nevertheless influenced employers in these areas.

“Our survey and field experiments show statistically significant evidence of hiring bias originating from information candidates shared on their online profiles," she noted. “Both by itself and controlling for a host of demographic and firm variables, our Muslim candidate was less likely to receive an interview invitation compared to our Christian candidate in more politically conservative states and counties.”

Religion was where most of the bias occurred. Both survey and field experiment by the researchers detected bias based on religion but not much change based on sexual orientation. Interview rates were similar for gay candidates as for those who identified themselves as straight, showing that the U.S. has come a long way on the topic of sexual orientation.

Religion, on the other hand, still matters.

“Employers' use of online social networking sites to research job candidates raises a variety of notable implications, since a vast number of job candidates reveal personal information on these sites that U.S. employers can't ask in an interview or infer from a resume," said Alessandro Acquisti, associate professor of information technology and public policy at CMU's H. John Heinz III College.

So if you’re looking for a job, be mindful of areas where there might be discrimination. Social networks do, in fact, influence employers.