Perhaps because of either its absurdity or its simplicity, a messaging app called Yo, which doesn't do much more than send a contact a voice recording of someone saying "Yo," has gone viral this week.

"Yo is a single-tap zero character communication tool," a description for the app reads on its Google Play and Apple App Store download pages. "Yo is everything and anything, it all depends on you, the recipient and the time of the Yo."

But Friday, several programmers said they had found ways to hack Yo to extract people's phone numbers and send other types of messages, revealing one of the problems with trying out an infant app. Yo acknowledged the security Relevant Products/Services holes.

"We are working on the securities issues that came to our attention," the app's Twitter page said Friday morning. "We want you to know we take this very seriously."

Yo's co-founder and Chief Executive Or Arbel told the Financial Times that he had raised $1 million to work on the app for the next year. The idea for sending people Yo's came from Moshe Hogeg, founder and chief executive of image-and-video sharing app Mobli. Hogeg wanted a simple tool to contact his personal assistant, Arbel said. The investment came from Hogeg's angel fund.

On Thursday, Hogeg posted on Twitter that the app had nearly 300,000 users and had soared this week to become the top free social networking app on the Apple App Store. The day before, Arbel reported the app had 60,000 users.

Yo does have at least one other feature that it's hoping to expand. Add "Worldcup" as a contact and send the account a message once, and Yo promises to send you a "Yo" every time a goal is scored in Brazil. Arbel told the Financial Times that, among other use cases, he sees retailers sending fans a Yo to alert people about sales. Like the well-placed head nod or wink, Arbel sees the Yo as more of a necessary communication tool than a novelty.