Lee Rainie, Director of the Pew Research Center, poses for a photograph, Wednesday, Sept. 4, 2013, in Washington. Americans might be sharing more personal information online than ever through social networking sites and email. But they also want to protect who gets access to that data and think they should be given better control of it, according to a study released Thursday, Sept. 5, 2013, by the Pew Research Center's Internet and American Life Project. (AP Photo/Alex Brandon)

Americans are sharing more personal information online than ever, but they also want to better control who can see it, according to a study released Thursday by the Pew Research Center's Internet and American Life Project.

The study says privacy concerns are growing, with 50 percent of Internet users saying they are worried about the information available about them online, up from 33 percent in 2009. Meanwhile, 86 percent of people surveyed have tried at least one technique to hide their activity online or avoid being tracked, such as clearing cookies or their browser history or using encryption.

People cite various reasons. About one-third said they had tried to conceal their activity from hackers or criminals, while 28 percent have tried to block advertisers. Others said they wanted to keep information private from family members or spouses, employers or the government.

"People choose different strategies for different activities, for different content, to mask themselves from different people, at different times in their lives," said Mary Madden, a senior researcher at Pew. "What they clearly want is the power to decide who knows what about them."

The report comes after a national debate erupted again over privacy and national security when a former National Security Agency contractor, Edward Snowden, leaked details of secret programs.

The study found that 68 percent of people agreed that the law is insufficient to protect their privacy.

Lynn Boyden, an information architect in web services at the University of Southern California, poses with a dating website on her computer at the USC information technology services center in Los Angeles Wednesday, Sept. 4, 2013. Boyden says she has developed two identities online: a public one for her professional life and a private one that only a few close friends can access. She tries to block advertising trackers when she can and limits what personal data might wind up on public sites. (AP Photo/Reed Saxon)

The Pew study, done with help from Carnegie Mellon University, is based on data from 792 Internet and smartphone users contacted by telephone by Princeton Survey Research Associates International from July 11-14. The margin of error is 3.8 percentage points.