Yo, the absurdly simple app that lets users message each other with the word “yo” (and nothing else), has allegedly been hacked by college students, putting the phone numbers of its users at risk.

Or Arbel, the app’s creator, confirmed to Mashable earlier today “a few guys tried to hack” the app overnight and “did succeed to some extent.”

“Some of the stuff has been fixed and some we are still working on,” he told TechCrunch. “We are taking this very seriously.”

Three Georgia Tech students revealed to TechCrunch that they were behind the hack.

“We can get any Yo user’s phone number (I actually texted the founder, and he called me back.),” one of the students emailed to TechCrunch. “We can spoof Yos from any users, and we can spam any user with as many Yos as we want. We could also send any Yo user a push notification with any text we want (though we decided not to do that.)”

The news of the hacking comes just as Yo cracked the top-five free apps in the iOS app store, surpassing Snapchat, Instagram, YouTube, and Facebook. The messaging app has also become a silicon valley darling, albeit a controversial one, attracting $1 million in funding according to a recent Financial Times report.