It's the bird-themed game that has the world in a flap, and while it's making millions angry, it's not Angry Birds.
Flappy Bird is a devilishly simple, phone-smashingly frustrating game in which you guide a small yellow bird through an endless series of gates simply by tapping the screen over and over again.
The free app has gone gangbusters in the past couple of weeks, leaving many around the world scratching their heads.
It sits atop Apple's app store in 89 countries, including New Zealand, Australia, the US and Britain, according to app analytics website Appannie.com.
On the competing Google Play store, it's the top-ranked app in nine countries, and close behind in dozens of others.
Flappy Bird's rise over the past month has been meteoric. It hit top overall spot on the app store on January 28 - a position it has held ever since. A week earlier, it was ranked below 1400.
In the US, the app has held No.1 spot since January 17 - a rise of more than 300 places from the beginning of the year.
Flappy Bird's astonishing rise is all the more bizarre given the polarising emotions it stirs.
"This app is the bane of darkness," says one of the more than 13,000 Australians who have reviewed it on the app store.
"It destroys you mentally and physically," the user writes, even while scoring it a full five stars.
Writes another five-star reviewer: "Don't download, don't exit the app, just drop your phone and get out.
"I haven't slept in five days, and I've lost all feeling in my fingers."
Adding to the curiosity is the game's humble origin. It's the product not of a multimillion-dollar studio, but a single Vietnamese developer known as Dong Nguyen, who did not return emails.
Its rapid and unlikely rise has led some in the blogosphere to speculate about foul play such as the possible use of bots - computers that masquerade as human downloaders - to boost download counts.
But Sam Yip, an industry analyst at research firm Telsyte, says it's not unusual for a game to explode in the way Flappy Bird has.
The big viral games such as Angry Birds and Candy Crush nail two crucial elements, he says.
First is the "boredom market". They're excellent time killers that can be played over and over again.
Second, they incorporate social elements. Users are encouraged to compete with one another and share their exploits via social media.
"These are the two things that can really make a viral game work and get it out there," he says.
It's tough to nail down why a given game goes viral at a specific point in time, he adds, but Flappy Bird was probably helped by the holiday season.
"Generally screen time increases at that time of year for certain demographics because of the extra disposable time people have."
But Yip also cautions that viral games can drop off the radar just as quickly as they emerge.
For many who have been sucked into the love-hate world of Flappy Bird, that may come as a relief.