The National Security Agency isn't the only federal agency that conducts surveillance on the internet. For decades, the FBI has been doing it as well.
As this 2016 Wired article details, the FBI initially started conducting online surveillance back in 1998, using a tool called Carnivore, which it installed on internet network backbones with the permission of service providers. The tool enabled agents to monitor the online communications of a person who was an investigative target, filtering and copying metadata and the content of messages that they sent and received. The Carnivore program's existence was exposed in 2000 when an internet provider refused to install it. As it turned out, the bureau had only used the tool 25 times up to that point, which indicates that it engaged in widespread spying. In 2005, the FBI replaced Carnivore with commercially available filtering software [source: Zetter].
Additionally, the FBI has other ways to tell what a person is doing on his or her computer. It can break into the machine, either remotely or by breaking into someone's office, and install key logger software, which enables agents to monitor what a person types on the keyboard. That trick makes it possible to circumvent software encryption tools that are designed to protect emails and other messages from being intercepted [source: Zetter].
The FBI has other tricks for unmasking people who visit child pornography websites and other places where bad stuff happens. The bureau's own hackers can gain control of servers and embed spyware on pages on a site, which in turn infects the computers of people who access those pages [source: Zetter].
Those capabilities might seem scary, but they're probably not something that most law-abiding citizens will ever encounter, let alone have to worry about. In the next section, we'll look at a type of tracking that you're more likely to encounter.