Found out someone had stolen my credit card info. My credit card company alerted me about it, and I reported it as fraud.
I feel I'm really careful about using passing around financial information, but I have no idea how careful the businesses I pass it to are, and so when something like this happens, it's hard to point at a likely source.
I do know that I used at least one new business the day before the fraudulent charges started. I should have no problem avoiding them. But it could also be something really complex, like someone at a local business just trading my number somewhere online.