There is a mysterious character named "Master" that has been defeating many of world's top players in Go, an ancient strategy game.
It turns out that "Master' is the updated version of AlphaGo, which is an artificial-intelligence program developed by the DeepMind unit of Google.
AlphaGo made history by beating the top Go player in South Korea last March. It won 4 out of 5 games.
Now under the disguise of a different name, it has defeated the world champion.
Go is a game invented around 2,500 years ago in China and is still a popular game across East Asia. Players take turns placing black and white stones on a grid as they seek to capture patches of territory by surrounding them.
The arrival of "Master" in China has shaken human Go players, upending thousands of years of the game's strategic wisdom.
"After humanity spent thousands of years improving our tactics, computers tell us that humans are completely wrong. I would go as far as to say not a single human has touched the edge of the truth of Go," said the world's reigning Go champion, Ke Jie.
Ke had already known in advance that "Master" was AlphaGo, but had to keep it a secret until it was announced by Google.
"Master" puzzled its human opponent by using a strategy of placing pieces in unconventional positions early in the game. It also changes tactics from game to game and will sometimes skirmish with its opponents across the board. Other times, it will also relinquish territory with hardly a fight.
Demis Hassabis, the chief executive of DeepMind, wrote in a tweet: "Over the past few days we've played some unofficial online games at fast time controls with our new prototype version, to check that it's working as well as we hoped. We're excited by the results."
He also wrote on Twitter that AlphaGo will return to more official matches this year.
"Master's" record is an undeniably impressive 60 wins - 0 losses over seven days via anonymous testing.