Not only is Yo stupid, it's now also a security risk

Yo! Remember the hit new app that managed $1 million in funding we covered yesterday, which enables smartphone owners to send "Yo" alerts to contacts? The service has been hacked by a student and two roommates. Yo has confirmed they're investigating the hack and expect to have the security vulnerability patched in the "next few hours". The hackers have been able to access any Yo user's mobile number with the ability spam any user with multiple Yo messages.

source: androidcentral