This far exceeds the scope of any wiretap laws we currently have in place. Second, analogizing pen register information from a traditional land-line phone system to the Internet is incorrect. The Carnivore system likely can capture content as well as numbers. Email addresses for example are personal to an individual rather than to a particular household. We don't know for sure, but it is possible that Carnivore has access to the subject line information of email messages.
Subject lines are content.
Carnivore can also track other content information such as the URLs of web sites visited. Seeing the URLs not only give routing information but content as well. Systems like Carnivore have the potential to turn into mass surveillance systems that will harm our free and open society. Currently, there is little if any public oversight over the FBI's use of its Carnivore system. The FBI has not allowed the ISP to inspect the device, nor have any of the advocacy groups been allowed to examine it.