The Senate Commerce Committee held a hearing on Wednesday about the privacy implications of online advertising. Present for Congress’s first real consideration of the issue were representatives from big-name internet companies such as Google, Microsoft and Facebook. In addition were privacy experts from the Center for Democracy & Technology and the Competitive Enterprise Institute, who followed up the hearing with a heated discussion on the PBS News Hour.

Google argued that advertisements, their main source of revenue, are what allow them to keep the bulk of their services free for customers. Targeted ads, they suggested, are also beneficial to customers because they don’t bog us down with largely useless information. Online shoppers or web surfers are exposed only to ads deemed relevant to them – or to what their data say about them.

So, what information do internet companies collect for advertising? On a typical search Google will collect your IP address, operating system, browser type, requested search query and cookies. Although generally none of the information collected is personally identifiable, internet users are still largely unaware of internet companies’ – and third-party advertisers’ – collection methods and use of their information.

But, while the ads that often bombard the tops, bottoms and sides of our computer screens sometimes seem a bit eerie to the average user, privacy experts have even greater concerns. Is any of the information personally identifiable? Even if it isn’t, could enough small pieces of that information be combined to paint a big enough picture that could be used to identify us personally? Could it then fall into the wrong hands or become public?

Congress is exploring new federal privacy protections that would make data collection more transparent and secure. They are looking to set a baseline for how information can be gathered and used; for example, limiting the use of information to the purpose for which it was originally collected.

The Pew Internet Project has explored consumers’ awareness of their digital audit trails in two recent reports, “Privacy Implications of Fast, Mobile Internet Access” and “Digital Footprints.”