An N64 emulator app for Xbox One was released and then quickly removed from the console's marketplace.
Word of the app - named Win64e10 - spread yesterday via Reddit, although it had actually launched quietly over the weekend.
While available, it cost £7.69 to buy Win64e10 in the UK.
The app was hidden on the marketplace as it had not received a Microsoft-approved release - but was searchable by name if you knew of its existence.
Microsoft obviously took note of the launch: the app is no longer available to buy now.
Regardless, anyone who did hand over money can still use Win64e10.
The legal grey-area app works by loading almost-certainly illegal ROM versions of games downloaded from the internet which you then copy to OneDrive, Microsoft's cloud-based storage system. You can then re-upload the files after playing with your latest save data.
Various videos exist on YouTube showing the emulator in action - it seems to work just fine.
It's not the first time an emulator has appeared on the Xbox One store - a NES emulator popped up earlier this month.
Microsoft updated Xbox One's firmware over the summer to technically support any Universal Windows Platform app from the Windows Store - although the company is clearly taking a far closer level of control over which apps get a formal Xbox One release.