Stolen was an instant hit thanks to its addicting gaming elements, where players can “own” their Twitter friends and trade them like baseball cards. Tech journalists, venture investors and teens quickly adopted it. Even Twitter COO Adam Bain had been a top player of the game.

Hey, Inc., the company behind the app had an interesting backstory: After building a few successful gaming apps, they had tried, for four years, to make their social media app take off. But it failed, and before they ran out of money, they returned to their gaming roots with a Hail Mary — Stolen.

But the team hadn’t planned for a viral success. They had to scramble to build moderation tools to keep bullying, profanity and pornography out of the game. The ability to assign a nickname to the accounts you own could quickly descend into online harassment. Hey, Inc. quickly built the ability for users to opt out of the game, and turned off the nicknaming feature on Wednesday.

But that did not appease U.S. Representative Katherine Clarke (D-MA). On Thursday she wrote a letter to Apple and Twitter with concerns over bullying in the app. She expressed concern over the language around “owning” someone else without their permission.

Not long after, Stolen’s creators pulled the game from the Apple (AAPL) App Store.

In a message to Fortune, Siqi Chen, CEO of Hey, Inc., says, “People had concerns about their safety and being stolen on their app and we are trying to do the right thing.”

It’s easy to see why it might feel like a violation of one’s identity to learn that people are buying and selling them inside a game they’ve never played.

“Overall our perception has gone from a fun game about collecting people you love to human trafficking and we’re horrified by that as well,” Chen says.

So what does it mean for the future of the company, which previously raised $7.5 million and is nearing the end of its runway? Chen says he’s confident they’ll find another hit.

“What got us this far is the persistence of our team, so we are still going and doing everything we can to make the company work, regardless of Stolen,” he says.

My letter 2 Twitter & Apple abt my concerns w/ "Stolen!" – an app that enables online abusers 2 “own” ppl’s profiles pic.twitter.com/c4ujmIq4e5

— Katherine Clark (@WhipKClark) January 14, 2016

The app is no longer available in the App Store. We've heard everyone's concerns and have decided the best thing to do is to shut down.

— The App That Used To Be Stolen (@getstolen) January 14, 2016