Representatives from the three companies -- each of which have raised concerns over privacy with their practices -- went before the Senate Commerce, Science and Transportation Committee on Tuesday.
The committee convened to discuss consumer privacy and whether online companies' practices of tracking people's activity and sharing that information with third parties violates it.
Committee Chairman Sen. Jay Rockefeller, D-W.Va., compared the practice of collecting information about people's behavior online to going into a shopping mall and having every move a person makes recorded, analyzed and shared with other people.
"This sounds like something fantastic, out of science fiction," he said. "But this fantastic scenario is essentially what happens every second of every day to anyone that uses the Internet."
Rockefeller said that it's likely many people don't know the extent to which online companies are collecting information about them, neither are they "empowered to stop certain practices from taking place."
"Do consumers realize computers are tracking what streets they walk on and what websites they visit?" he asked. He also questioned what benefit this sort of activity is to the web users themselves.
Generally senators expressed dismay over the scenario Rockefeller painted and stressed that privacy practices have to be taken seriously because many people are unaware of how their online activity is being tracked and used.
The panel convened as the Senate considers whether legislation is needed to protect personal information people share online from misuse. Congress is not expected to pass such legislation this year, but lawmakers expect it will be a priority for consideration in early 2011.
The issue has been especially thorny lately for the three companies given controversy over Google's collecting unsecured data from private Wi-Fi networks, Facebook's ever-changing privacy settings and the leak by AT&T of more than 100,000 email addresses of Apple iPad users.
In their defense, company executives told the panel they believe they are adequately informing people how their information might be used, and are as concerned about privacy as lawmakers are.
"Apple is strongly committed to giving our customers clear notice and control over their information, and we believe our products do this in a simple and elegant way," Guy Tribble, Apple's vice president of software technology, told the committee.
He said Apple shares the concerns of the committee about the collection and misuse of data, particularly privacy data.
Facebook's CTO Bret Taylor said that the company gives users what they need to control the privacy information, and that keeping track of how they behave online is crucial to the content of the site itself and how they use it to achieve Facebook's goal of linking people up online.
"The people who use Facebook … are the driving force behind the continued innovation and constant improvement of our service," he said. "Our goal is to make it simpler for people to connect and share, and to give them the tools to control their information."