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Here's what Hanke has to say about those apps (emphasis ours):
"Yeah, I don't really like that. Not a fan. We have priorities right now but they might find in the future that those things may not work.
"People are only hurting themselves because it takes some fun out of the game. People are hacking around trying to take data out of our system and that's against our terms of service."
As Kotaku's Patricia Hernandez points out, lots of players are only turning to these tools - largely used to show, on a map, where Pokémon are appearing and when they'll vanish - because the game's own system for tracking Pokémon have been broken for about two weeks now.
But, as Hanke notes, those tools are very much against Niantic's terms of service, which every player agrees to when they create their Pokémon Go accounts. Niantic would be well within its rights to turn off those external services, if and when it chooses to.
Screenshot/PokeVision
As for Hanke's argument that using those tools "takes some fun out of the game" - well, that's largely for players to decide. But so long as systems like the Pokémon Nearby tracker aren't working, it'll keep driving people to those unauthorized tools.
In the meanwhile, as Hanke says, Niantic has "priorities right now," likely referring to its effort to bolster the game's servers so the Pokémon tracker can start working reliably again. So it might be some time before Niantic has enough free time and manpower to start worrying about unauthorized apps.