Only happened once to me. My bank called around 8:00 on evening.
There was a small ($1) charge they thought was suspicous.
They put a smack down on it and sent me a new card in a couple days.
Alot of these guys will run the small charges to verify that the card number is valid. Since alot of banks do this also to check accounts, the under 1 dollar amount is always looked at with suspicion because it usually is reversed after confirmation of activity.
This way, they know that they have a valid working number and can run alot of charges thru quickly before it gets shut down.
Dave