Privacy advocates say they worry how Facebook will use information on Web page visits of its estimated 800 million members. The social networking site, whose profits come primarily from advertising, had been vague about its collection of tracking data. But it now acknowledges it can use cookies to create a 90-day log of where each of its members have gone on the Web after visiting a Facebook page, USA Today reports. Privacy advocates want consumers to be able to stop or limit tech companies and ad networks from tracking them online but the advertising industry wants to keep the existing system. But while privacy advocates express concern the Facebook tracking information could be sold to third parties, Arturo Bejar, Facebook\'s engineering director, said it uses the data solely for security and to improve \"Like\" buttons and other plug-ins that allow users to log in to Facebook from millions of Web pages. Facebook has \"no plans to change how we use this data,\" company spokesman Andrew Noyes said. The site\'s plans, he said, \"stand in stark contrast to the many ad networks and data brokers that deliberately and, in many cases, surreptitiously track people to create profiles of their behavior, sell that content to the highest bidder or use that content to target ads.\" USA Today noted new online privacy guidelines are being worked out in Congress and by the World Wide Web Consortium, which sets standards for the Internet. Facebook \"should be covered by strong privacy safeguards,\" said Rep. Ed Markey, D-Mass., co-sponsor of a bill designed to limit online tracking of children. \"The massive trove of personal information that Facebook accumulates about its users can have a significant impact on them -- now and into the future,\" Markey said.