This happened to me on my Capitol One card. I saw 2 bogus charges - one to AOL and also to some webhosting company. I promptly called both to investigate.

AOL had a great fraud department and found that the application which used my card had random data in all of the data fields (name, address, etc) How my card passed through that one is a mystery to me. Anyway, they refunded my card the ~$30 fee.

The webhosting company was just amazed that it happened. I requested logs and info about which domain was purchased with my card, but they never followed through on anything.

Capitol One was really good about it. They refunded me and gave me a new card. I doubt they ever did much further than that though. I would have liked to have found out which bastard got my card number, etc.