The Yo app has raised $1m (£600,000) in funding
Messaging app Yo, which in the past week has rocketed to the top of the app download charts, has been hit by a hack.
Creator Or Arbel told technology news site TechCrunch the app was having "security issues".The app allows users to send a message saying "yo" to friends - and nothing else.
It has been branded "pointless", but has nonetheless raised $1m (£600,000) in investment.
TechCrunch said it was contacted by three college students who said they had uncovered a flaw in the app.
"We can get any Yo user's phone number (I actually texted the founder, and he called me back)," the students told TechCrunch.