In that game, you have six tries to guess a five-letter word and can brag on Twitter if you win. It was created in October by former Reddit software engineer Josh Wardle and is available to play only once a day on his website.

In December, Wardle added a “share results” feature and players jumped to more than 300,000 from 90 by Jan. 1, according to the New York Times. Then, Fallon told his 51.4 million Twitter followers that he was addicted. Wardle didn’t immediately respond to a request for comment.

As the term “Wordle” began trending and news outlets picked up on its popularity, other versions for mobile devices started to catch on.

Over the weekend in Apple’s U.S. App Store, two Wordles shot up the charts in the Word category. At No. 8 is Wordle!, a time-based game created by developer Steven Cravotta, which was launched in the U.S. App Store more than five years ago.

At No. 13 is Wordle, which Candyblocks launched this month. The game offers 1,000 levels to play through, according to its description. Wordle – Daily Word Games!, also released this month by Mediaflex Games, is at No. 58.

In the past, Apple has taken down clones of hit games. When the developer of the viral sensation Flappy Bird pulled his game in 2014, it continued to live on in meme games until Apple took action.