Leaks happen all the time, it's common with this industry. Sometimes the leaks happen thanks to a developer leaving a laptop with confidential files on it on a plane or someone snaps a couple pictures of an early build of a game and uploads it to Twitter. A massive leak almost happened for Microsoft in a very hilarious way, luckily for them, the person who could've leaked it had a kind heart.
In March 2013, a man named Jia Li ordered a new laptop from Microsoft but instead of recieving a brand new laptop, they came into possession of an Xbox One. A console which had not been formally revealed at the time. Li wasn't able to identify the console as an Xbox right away as any sort of Xbox logo was covered (to prevent leaks) and the boot up screen had the word "Kryptos" instead of "Xbox One". Li knew this was obviously a mistake and that he probably shouldn't keep it, but he wasn't going to let this thing go without taking some pictures.
Li eventually gave the prototype back to Microsoft after reaching out to them and handing it back to a Microsoft representative who came to his home to pick it up. Li was given an Xbox 360 and the laptop he originally ordered as a reward for returning the machine.
How did this happen though? Microsoft was storing the prototypes in a shipping warehouse of all places, probably thinking that's the last place people snooping around would look. Someone mixed up the order somehow, and the rest is history.
