The Cortex was a complex interplanetary computer network comprised of nodes and access points. An IdentCard was typically required to use the Cortex, and all activities were monitored to some degree. A private link was available to the wealthy via a dedicated source box, and public access was available in a pay by the minute scheme. The Cortex could also be accessed by a ship's computer or by a personal encyclopedia. ("Serenity (pilot)", "Safe", "Our Mrs. Reynolds", "Firefly - Big Damn Hero")
People were also known to connect to the Cortex illegally, co-opting someone's account or hacking into a public terminal with false credentials.
It was possible to locate someone within a ship's orbit via node tracking—but from there, unless they were using landlines to connect, it was very difficult to pinpoint someone's location with only a Cortex trace.