Leaking in games

Leaking happens when content from a game/project, or even the entire game/project itself, is made public earlier than intended by the game's developers. However, it may also happen long after the game/project was originally released (i.e. 20 years after the initial release). These types of leaks however, usually only contain source code (which still is disrespectful to the original developers).

Reasons for Leaking
The reasons for leaks can vary. Leaks close to the actual release can occur when pre-orders are shipped to the recipients days earlier. Nowadays with the advancement of the internet, many streamers and YouTube users take advantage of situations like these and are sure to stream a whole playthrough of the game.

Whole games can also be leaked by staff of the game development team, reviewers that were given copies of the game early before release, or retailers. These usually surface in form of dumped ROMs or as archive by groups of the cracking scene.

Other reasons can be oversights from the developers themselves. Demo versions usually aren't created from scratch but instead reflect the current state of the main game trimmed down to a small presentation. Dataminers are quick to look for leftover content and clues that can spoil to various degrees.

Examples

 * 1) Half-Life 2 leak: Perhaps one of the most infamous leaks in the gaming industry. The [late] beta (as well remains of mid-late alpha) version was stolen by Axel Gembe and leaked to the internet. The result was $250 million in damage to Valve, which forced them to cut much of the leaked content in the current/final version and making the game short than in leak version was and forced them into an additional year of development of the game (as it was originally to be released in November 2003).
 * 2) The Last of Us Part II: More information could be seen here.
 * 3) mh:awesomegames:Super Mario Odyssey: On October 23, 2017, people leaked the game as many people used the game on YouTube and Twitch.
 * 4) mh:awesomegames:Sonic Mania: On August 11, 2017, people leaked the game as many people used the game on YouTube and Twitch.
 * 5) Sonic Forces: On October 27 2017, people leaked the game as many people used the game on YouTube and Twitch. The largest one since Sonic Generations.
 * 6) ROMs for Pokemon Sun and Moon were leaked online allowing people to pirate the game before its official release. Nintendo responded by permanently banning any 3DS system with a pirated ROM that tried to go online.
 * 7) Pokemon Ultra Sun and Ultra Moon: on 8th November 2017, people used ROMs to leak the game as many people used it on YouTube and Twitch, like its predecessor. Even the official YouTube page leaks a big chunk of the games! Nintendo responded by permanently banning any 3DS system with a pirated ROM that tried to go online.
 * 8) mh:awesomegames:New Super Mario Bros. Wii: A 24-year old Australian leaked the game, which leads into a lawsuit that Nintendo won and received $1.5 million as a compensation.
 * 9) Yoshi's Crafted World: Before the name was officially revealed at September 13, 2018. Nintendo accidentally leaked the official name of Yoshi's Crafted World after the Nintendo Direct's delay in September 6, 2018. After the official name was leaked, people all over the internet spread the name like wildfire ruining the surprise for a lot of people.
 * 10) Just Dance 2018: On October 20, 2017, people leaked the game on YouTube and Twitch.
 * 11) Call of Duty: Black Ops 4: It had so many leaks back before its relase that Activision could've just flat out reveal its features by that point. As the number of players are in the "Blackout", the Black Ops pass and many others had been leaked already.
 * 12) Crash Bandicoot 4: It's about Time: It also got so many leaks that Activision just announced that the trailer of the game is coming at Summer games festival of 2020, the title was revealed a lot and many assumed it's fake until the leaks started increasing to the point that Activision themselves gave up and said it's real.
 * 13) Mario + Rabbids Kingdom Battle: Rumors began spreading around Ubisoft's Rabbids and Nintendo's main mascot Mario having a crossover for the Nintendo Switch in November 2016. Then it popped up again in May 2017, where Kotaku reported that they received real art assets from their source but were told not to share them. The game's art assets were leaked in May 23, 2017 along with marketing and other presentations to the public which cause the game to face major backlash over the odd concept between Mario and the Rabbids (not to mention, people who seen the the leak were overreacting about Mario holding a gun along with the cropped Rabbid Peach that started the leak). In E3 2017, the game was in fact real when Ubisoft revealed the game at their conference which was praised "Best Strange Game" for the year.
 * 14) Prior to its release, Mortal Kombat 11 had a bad amount of leaks, which included Kronika's fatality, the return of Frost, microtransactions, the entire story mode, etc.
 * 15) mh:awesomegames:Super Smash Bros. Ultimate: This game has been hit big time with leaks, one person named Vergeben spoiled half of the newcomers before they were revealed, the entire first direct at E3 was leaked, and lastly the entire game was spoiled two weeks before launch, this also led to Crunchii's channel being terminated for good.
 * 16) Several copies of mh:awesomegames:Kingdom Hearts 3 were stolen around mid-December 2018, one month before its release, and sold on Facebook marketplace, which in turn caused leaks of several major parts of the game. Square Enix's response was to cut the game's secret ending and epilogue for physical copies of the game, which were added back in with a day-one patch after the game's release.
 * 17) Pokémon Sword and Shield: On November 1, 2019, people have leaked various Pokémon that haven't been revealed yet and many other stuff, such as some elements of the story, being spoiled online. The leak also revealed that the models for the returning Pokémon are the same ones from the 3DS games, despite Game Freak claiming they were made from scratch.
 * 18) mh:awesomegames:Animal Crossing: New Horizons: On March 17th, 2020, many people, including an infamous Splatoon YouTuber named Samuel Bessega Switch, obtained pirated ROMs of the game and were able to play and livestream the game on YouTube and Twitch 3 days early before the game's release date.
 * 19) Images of Resident Evil 3 (2020): Were leaked onto Twitter several days before Capcom announced the remake, which spoiled the surprise for many.
 * 20) Pokémon Café Mix: Many of the unreleased Pokemon, were leaked by dataminers before the game was released. Causing those Pokemon to not appear in the game for a while.
 * 21) mh:awesomegames:Sonic the Hedgehog 2 was leaked twice before its release; the first time was an early alpha that was spread around Brazil and China, and the second time was on November 9, 1992, when the CENSOR group leaked a late beta. Fortunately, the second leak was forgotten about.
 * 22) The Last Of Us Part I: A remake of the first game in the series, many assumed that this is fake because many believed it is to soon for a remake of the first game, however the rumors started growing until it was confirmed.
 * 23) Sonic Frontiers: Despite a few info of the upcoming open world sonic game has been revealed by the game's makers (i.e, the situation sonic got himself into, the open world...er open zone location, the combat, etc.) Leaks had been showing up from 4Chan, ranging from a skill tree, EXP making, and a BOTW shine style activity called "cyberspace".
 * 24) Saints Row (2022): The reboot of the Saints Row series has been hit with gameplay and story leaks two weeks before the game's release, up to and including the final mission.

Why This Practice Sucks

 * 1) Similar to spoilers, leaking a game can kill hype for many players and could even turn some people away from playing it.
 * 2) People who leak these games usually only do it to get attention and fame.
 * 3) It's disrespectful to the authors and developers who make these games, even worse for presentations.
 * 4) This can also happen from the game dev's being incompetent and careless about the information and end up giving it away.
 * 5) People who leak games can end up in huge trouble, such as a heavy fine, a lawsuit from the game company or a permanent ban from online play.
 * 6) Some leakers would leak unrevealed game footage and major plot details and get away scot-free from punishment (MrBossFTW being a prime example of this).

The Only Redeeming Quality

 * 1) A few games that were cancelled during production were found and bought into the public from leaks.

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