My card just got cancelled yesterday by Barclaycard.
They received information from the fuzz who had recovered a list of card numbers somewhere, so instantly blocked my card.
New cards within 5 working days, bit of an inconvenience at this time of year but much less of an inconvenience than trying to sort out the alternative.
I never let my card out of my site and always look for anything suspicious when using the various swipe machines and card readers. Who knows how it happened but at least the CC companies are doing a good job of protecting us.