Sonic The Hedgehog is a platform video game published by Sega for the Sega Mega Drive/Genesis. First release in 1991, it was the first installment in the Sonic The Hedgehog series, and it was released to widespread critical acclaim. 
Sonic the Hedgehog 1 Genesis art



A very well-known myth arose a few years after the release of the game. According to the story, there was apparently a bootlegged version of the game that appeared to be the same game on the outside, but whose gameplay was vastly different. In this supposed bootlegged game, a demon-posessed Sonic chased down other characters of the game in twisted, fire-filled worlds. 

Although Sega has never commented on this popular legend, there is still a small but persistent group of players who believe there is a modified version of the game out there.

Due to the popularity of this urban legend, some very devoted players made a fan-made game based on the sonic.exe legend.