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In Sharon's dream world of Harry Barker, a debugger is an artificial intelligence in the form of a menacing, cloaked, hovering figure with emaciated hands and arms, no apparent legs or feet, and no visible face. Possibly created as a hacker tool to aid in eliminating programming errors, these "creatures" have since morphed into dangerous "beasts" whose "whole reason to exist is to tell hackers everything they do wrong." They attack a hacker's confidence by fostering insecurity and self-doubt. The most effective defense against a debugger attack is the Oculus hack, which "projects a VR construct to act as a shield or, in its most powerful form, a distraction to scare attackers or give [the hacker] time for escape." The Oculus hack requires a great deal of self-confidence to pull off, which in turn helps defeat the debuggers' chief form of attack.
During Harry's third year at Hollerith's, he was attacked on the train ride to school by a debugger searching the train for the escaped "murderer" "Serious" Nick. He was rescued by Dwayne Duncan, who repelled the debugger using the Oculus hack. Later, during a lesson in Dwayne's Defense Against the Dark Arts class, a bogon transformed itself into a debugger, frightening Harry to inaction. Again, Dwayne stepped in and repelled the bogon. After class, Dwayne revealed to Harry that by seeing the bogon as a debugger, Harry's greatest fear was fear itself. Dwayne began tutoring Harry in how to use the Oculus hack, again using bogons as a substitute for the real thing.
After confronting "Serious" Nick and Petey Petagrue in the Spamming Shack and learning the truth about what happened between the two, Harry chased after Nick to find him being attacked by debuggers, which sapped Nick's will to live. Harry attempted to rescue his godfather but blacked out in the process. Later, Harry and Harmony used a GOTO function to travel back in time to attempt to rescue Nick. When they witnessed the debuggers attacking again, Harry used the Oculus hack to repel the creatures, realizing that he must have rescued his past self and Nick earlier, thus giving himself the confidence to do it again.
Debuggers are analogous to the dementors of Harry Potter. They are based on real-life debuggers, computer programs that are used to identify flaws in other programs. They are also based in part on Larry Wall's Three Virtues of a Great Programmer: Laziness, Impatience, and Hubris; by instilling self-doubt and destroying a hacker's confidence, they undermine the hacker's hubris.