Yo, a viral messaging app that arose from an April Fools joke, now has over one million users.

Last week, news broke that the ridiculously simple app had pulled in $1.2 million in angel funding. The app only allows users to send the word “Yo” to other users — similar to the functionality of Facebook’s original “Poke” feature —  and yet it appears to have surpassed the million user milestone.

According to the company’s official Twitter account, it surpassed 1 million users in four days:

This traction, however, may be short-lived, as disbelief and shock over the app’s existence fades. For now, the app still ranks quite high in Apple’s App Store, according to app store tracking site App Annie. Here’s a look at the app’s growth rate on iOS in the U.S. and overall:

Yo App Annie

For more on Yo, check out these six unbelievable quotes about the app.

Via: The Wall Street Journal.

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