This faux disease was spread to the public, and included a number of false symptoms to appear like any other illness. Descriptions of such symptoms may suggest it was caused by Radiation poisoning (ie. tumors, migraines).
Several members of the United Rebel Front claimed to have this condition, hoping to bargain with the UNSC to gain treatment for the condition in trade for some FENRIS Nuclear Warheads they had in stock. However, their status was false, as the bargain was revealed to be a trap set up by Howard Graves in an attempt to capture Spartan-IIs.
Staff Sergeant Avery Johnson's falsified Medical record - to hide his real, classified record - had him as a sufferer of Boren's, in which he was to have contracted the disease on Paris IV, after being in contact with a dangerously high amount of radiation apparently originating from a crate of captured Plasma Grenades.
This false record event (known to ONI as the Paris/BS Spoof) was likely used as a means of avoiding any investigation into his altered DNA (Radiation is known to work as a "Mutagen").
Untreated or unsuccessfully treated, Boren's can be fatal or debilitating. While some effects, such as migraines, can be managed with medication, the tumors involved in the disease usually, or possibly always, become malignant. Because of this, treating Boren's Syndrome invariably means treating cancer, a process that can be debilitating. The only way to cure Boren's syndrome is an intensive regimen of Chemotherapy lasting for thirty weeks.
According to theory, some combination of the disease's (apparently) multiple pathologies discourages Flood Super Cells. This would explain why Sergeant Avery Johnson could not be infected when he and his squad were ambushed by the Flood on Installation 04, leading Master Chief to his moral dilemma. Dr. Catherine Halsey guesses that there'd be a billion to one chance that Johnson's condition could be reproduced.
Technically, there is no explicit proof that Boren's Syndrome discourages Flood. It may be that the nervous system of someone with the disease simply cannot support Flood. One hypothesis is that an infection form attempting to latch on to a host with Boren's Syndrome would recognize the characteristic neurological disturbances as "irreparable damage," thus rendering the sufferer immune. However, it is highly likely that if this condition did in fact prevent Flood infection the Forerunner would have found it after hundreds of years of research into Flood prevention.