The official "Sonic.exe" game produced by MY5TCrimson on GameJolt is safe to download according to ESET, a large anti-virus software company. However, executable files from non-trusted sources can be dangerous and infect your computer with malware.
"Sonic.exe" originated as a story posted to the "creepypasta" wiki. The story describes a player discovering an altered PC port of the original Sega Genesis game. An increasingly unnerving series of events occur. A game based on the story was created and is available for free download. The game is a modified version of the Sega game and features many of the elements of the "creepypasta" story.