I bought a Klein Bottle¹ from Cliff Stoll, famous among oldsters for an early example of tracking down a hacker:

"One day in 1986 his supervisor asked him to resolve an accounting error of 75 cents in the computer usage accounts. Stoll traced the error to an unauthorized user who had apparently used nine seconds of computer time and not paid for it. Stoll eventually realized that the unauthorized user was a hacker who had acquired superuser access...”