Comment by kalleboo

I remember the stored-value transit cards in Sweden in the 90's/00's. They were just magstripe cards with the value on it and a basic checksum value. It was not hard to figure out how to rewrite the card with a higher value, or just clone it, value and all, onto a separate card. No online component, as mobile networks weren't great when the system was designed.

They'd download their transaction logs out of the buses every night and do a reconciliation. If they found a card where the value went up or had impossible travel times, they'd look at the travel routes/dates and wait around on the "hackers" commute route with a police officer until they showed up. Very manual.