Flappy Bird is the cheapest digital drug on the App Store

Flappy Bird is currently the most popular free app on the App Store, besting the likes of Snapchat, Beats Music and Clash of Clans. That's a pretty big accomplishment for a game that can be played with a single finger. So why is it so popular? Well, that's actually a bit hard to explain.

There's only one thing you ever do in Flappy Bird: Guide your tiny avian -- who happens to look a bit like a fish -- in between a series of pipes. Hitting a pipe or crashing into the ground ends the game. Tapping on the screen causes your bird to flap its wings and remain aloft. For each set of pipes you pass through, you gain a single point. Yep, that's the entire game.

This simplicity is remarkably addicting, and as soon as you fail, you're going to want to give it another go. The game's difficulty is shockingly steep right from the beginning, and making it through a few sets of pipes isn't nearly as easy as it might sound. After hours of play, your longest run will still likely be in the 30-point range.

Flappy Bird is free, but it is ad-supported. Unfortunately, these ads aren't exactly the most subtle. They appear as popup banners on the top and bottom of the screen and sometimes block the edges of the pipes themselves. It can sometimes feel like you're actively battling the ads just to proceed, which isn't ideal.

Thankfully, Flappy Bird's addictive properties make these ad issues worth overlooking, at least for a while. You may eventually get fed up, but you should definitely take the game for a spin, if for no other reason than to see what the buzz is about.