The creator of Garry's Mod has revealed that he intentionally added an error message to the commercial version of the mod, which only appears in pirated versions of the game.
Speaking on Twitter Garry Newman commented on how he, "Just enabled this error in GMod today. It happens when you pirated it. Having fun watching people complain." He then provides a link to Google searching for the error message "unable to shade polygon normals".
The error only occurs in pirated version of the utility, with the user's 64-bit Steam ID also forming part of the message. Newman has identified the pirates and locked them out of the illegal version, while also banning them from his forum.
Questioned by fans as to why he implemented the measure, Newman responded: "I don't think the error isn't going to boost GMod sales. I just like to give people that paid something to be smug about."
Although it first became popular in 2004 as a free download, Garry's Mod has been available on a Steam as an officially-licensed Source engine product since 2006.