I was in Tesco yesterday and my card was not accepted. Odd, I resolved to ring the card company when I got home. I forgot. Today I had a call - and I rang them back on their number (they were fine with that, unlike a previous company).
Yesterday there was a payment to someone like totaljobs.com for a few hundred pounds. This was following a transaction for 78p to some obscure place. It triggered some alarm bells with the card company and they froze things until they could talk to me.
The 78p was a test to see if the skimming worked.
I didn't authorise these transactions - somehow the card had been skimmed (amazing really, I never let the card out of my sight in shops and restaurants as I am aware of skimming possibilities).
Fortunately things had been caught, no money changed hands - unfortunately I now have to get a new card.
Tesco Credit card handled the whole thing pretty well.