It’s been over twenty years since the release of the original Red and Blue, but people are still messing around with the games to discover new glitches and exploits. It’s incredible.

Last week, we told you about a recent Red and Blue exploit that allows you to delete your opponent’s save files just by playing against them. This new exploit by MrCheeze is kinda like that, except with the opposite result. In this case, playing against another person will force their save file to replicate yours, thereby “infecting” them with a Pokémon virus. If the target goes on to play against someone else, that person will also get saddled with the virus. It’s like Pokerus, but real. The whole thing works on actual hardware, as you can see below:

The creator calls it the world’s first self-replicating program for a dedicated gaming system, which is a feat. MrCheeze says that the idea came to him a couple of months ago, after he figured out how to use a glitch within Red and Blue to beat an entirely different Game Boy title in record speed.

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“One commenter on that video suggested that that the whole thing was rather like a virus,” MrCheeze told Kotaku. “In fact the metaphor isn’t very accurate, since the player has to glitch Magi-Nation pretty heavily in order to get it to look at the leftover Pokemon data. But the idea of a virus was very evocative, and I started thinking about whether it would be possible to run arbitrary code that can actually spread from one copy of the game to another. And gen 1 Pokémon being gen 1 Pokémon, of course the answer is yes.”

The virus exploit took about a week to create, and it has now been released into the wild for others to tinker around with. The good news is that it is not a destructive exploit: instead, this virus allows you to edit your own party, which you can then upload to Pokémon Bank. MrCheeze says he didn’t make this to enjoy in-game benefits, however. The whole thing was more of a mad scientist operation.

“Sure, there are practical uses, like making custom Pokemon for sending to Sun and Moon,” MrCheeze said. “But really, this is more of a ‘because it is there’ thing—just knowing that something as crazy as this is possible is more than enough reason to want to try it.”