The Karnoffel Code is one of the primary elements of the Inscryption ARG, and is alluded to several times by various characters throughout the game.
In the ARG, it is revealed that the Karnoffel Code is a computer algorithm of supernatural origin and recovered by the Soviets during the Cold War after gaining possession of Adolf Hitler's corpse and discovering a conspiracy related to him, a deck of Karnöffel playing cards, a German card game, and the specific order the cards were arranged in. A spy named Barry Wilkinson had gotten a copy of the Karnoffel Code from the Soviets and sent it to Kaminski, who ran a data center in Germany, who hid it on a floppy disc among other empty floppies, which eventually fell into the possession of Kaycee Hobbes.[1][2] As such, the OLD_DATA appears to be a form of the Karnoffel Code, which in the game's narrative is connected to the seemingly supernatural corruption affecting the game Inscryption.
Certain characters ingame know about this code such as the Trapper/Trader, the Mycologists, Grimora, and the Bone Lord.
Additionally, one of the video sequences in the game flashes the binary sequence "0100101101000001010100100100111001001111010001100100011001000101010011000010000001000011010011110100010001000101", which translates to "Karnoffel Code" in ASCII.