Yo, the free app that only lets you send "yo" in messages to friends, is currently experiencing "security issues." After rising rapidly in popularity and entering the US App Store’s Top 10 list, TechCrunch reports that Yo has been hacked by three college students. The hack allegedly reveals any Yo users’ phone number, and enables message spoofing with the ability to send any text-based push notification to devices. Some Yo users appear to have received some of these notifications today.

Or Arbel, founder of Yo, has confirmed the security problems in a statement to TechCrunch, and notes that the company has addressed some of them. Arbel refuses to detail the exact fixes, but has promised the issues should be resolved in the "next few hours." While message spoofing isn’t a huge problem for a service that only supports "yo," the ability for hackers to link usernames and phone numbers could be a big privacy concern for those using their full names as usernames on the service. Snapchat was hit by a similar problem earlier this year, allowing hackers to publish details of 4.6 million phone numbers and usernames. The company behind Yo, Life Before Us LLC, has attracted $1 million in angel funding, so there’s really no excuses for such lax security measures.