Summary: The author of the article explains how they were able to use a user-controlled arithmetic overflow to buy millions of card packs for "free" in Magic: The Gathering Arena. They decompiled the game's code, found a function used to submit a purchase request using in-game currency, and noticed that the price was calculated by the client by multiplying the unit price of the item being purchased by the quantity being ordered. They were able to force a user-controlled arithmetic overflow to occur, allowing them to purchase millions of card packs without spending any additional in-game currency. The author notes that the value of the digital cards obtained is not the reward, but rather the knowledge gained from the process.