In the ongoing effort by developers and publishers to combat video game piracy, some developers program special features designed to only activate if the game suspects it has been pirated. Rather than simply crashing the game or blocking all progress, as DRM systems typically do, these features wait to activate until the player is in-game, causing any manner of effect, such as randomly deleting save data, creating increasingly obnoxious effects, removing vital in-game items and abilities, and more.
Note: in-game effects are not to be confused with in-game copyright protection, wherein portions of a game can only be progressed past if the player has a physical item bundled with the retail game.
A more comedic example, copies of Alan Wake after version 1.05 place a stereotypical pirate's eye-patch on Alan Wake's face. The game remains fully playable, however the eye-patch can not be removed, and the game's loading screen messages are replaced with messages asking that the player buy the game should they enjoy it.
Upon booting, Earthbound will display an anti-piracy message, but will not prevent players from proceeding into the game. However, in-game, enemy spawn rates are significantly increased, and approaching the final boss fight will delete all save data and crash the game.
Game Dev Tycoon
While not originally present in Steam copies of Game Dev Tycoon, Greenheart Games uploaded the game to piracy websites themselves, including additional code that would cause in-game software piracy to run rampant. This would directly impact sales of players' games, typically bankrupting companies in this version of the game after a short while.
This behavior was later introduced to the Steam version of the game under an optional challenge mode.
Michael Jackson: The Experience
As a nod to the memetic popularity seen by the oft-annoying vuvuzelas in 2010, the Nintendo DS version of Michael Jackson: The Experience plays off-beat vuvuzela noises constantly over in-game music if the game's DRM fails its checks. Additionally, in-game music plays in a much poorer audio quality, and notes no longer load, preventing any progression.
In pirated copies of Mirror's Edge, certain ledges slow the player down - almost to a stop - as they approach, making affected jumps impossible, halting any progress.
Serious Sam 3
Upon picking up the first pistol in Serious Sam 3, a scorpion will spawn that constantly follows the player, moves much faster than usual, and takes no damage. Additionally, the game is incapable of saving, and will crash randomly.