I had the exact same thing happen just last Saturday...debit card was rejected at grocery store....came home and checked balance and there was money in the account. I called the 800 # to see what was going on and come to find out my bank's security system had shut my card down because on the same day there was a charge from Brazil, Kennebunkport, MA, Nassau and TN ! Totaled about $110.
Fraud folks said that these folks are such good crooks they "phish" for account numbers and when they find one that is viable, they make a small charge, i.e., the charge from Brazil was only .69 ! They said even if your card never left your possession or was secure in your purse or wallet they can still get your information.
I've had card replaced and a new account number, but there is not guarantee this won't happen again next week.
The bank also said to place the bulk of your funds in an account that is not accessible via a card....which means you have to go to bank (or in my case, my computer) to move money around.