[schoen]

> There was a code path where you could send someone negative amounts of the currency and it would happily pay them a negative amount of currency and charge you a negative amount of currency, thus transferring their account balance to your against their will.

This is a bug I remember from the Apple II game "Taipan" (in which you play an 1800s opium-and-silk trader in East Asia). You could borrow negative amounts of money from a lender who charges extremely high interest. As a result, the lender would quickly end up owing you tremendous sums, without your having to do anything else. Wikipedia mentions this:

> Note: A bug in the original game allows the player to overpay the moneylender, acquiring "negative debt". This "negative debt" will accumulate interest very quickly, and will count towards the player's net worth. As the game's vocabulary of number words ends at "trillion", this can cause the game to display garbage instead of the player's correct net worth. This has been fixed in the online "for browsers" version of the game.