According to a report by Eurogamer, Nintendo repurposed an illegally copies ROM of Super Mario Bros. and resold it to the general public. Eurogamer did their own investigation with a “homebrewed” Wii, a hex editor, and the assistance from an independent emulation designer. The site came back wit the following results..
“The .NES header, originally created by Marat Fayzullin for his iNES emulator, is used to provide emulators with the necessary context needed to recreate a hardware setup that changed with each and every cartridge. Finding it in this Nintendo-published version of Super Mario Bros. felt like a sign we were heading in the right direction.”
Eurogamer then sent the files to Fayzullin and they concluded the pirated version was identical to the digital version distributed by Nintendo. Fayzullin did note there are some minor changes between ROM dumps. Stating..
“Depending on the cartridge version and how it has been dumped. If you see that your .NES file DOES NOT match any of the ones found online, it is likely to be their own ROM dump.”