A common trick nowadays is to buy gift cards - that was what happened to me when my card was used fraudulently. If it's exact dollar amounts (usually in multiples of $10, $25 or $50) then that's probably what it is. I know that my US Amex allows me to set up various alerts which are sent via SMS to my mobile phone and I would really encourage anyone else who has that functionality to use it. I had three alerts in short order saying that there was a "card not present" transaction approved and I was immediately able to block the card against further use. I also get alerts if there are large transactions etc.