You're definitely right with the security aspect of it... I knew someone who kept their pin number in their wallet with their bankcard, wallet went missing as did several hundred pounds. They hadn't taken out card cover so lost the money.
Last year I decided to pay off a credit card completely so I rang up with switch card and credit card in hand. I wasn't sure of the exact balance, but thought it was in the region of £1000 (had been on holiday). So, I asked them to read it out.. "Severn thousand, four hundred and..." Eh? Did I hear that right? I got the lady to read the last few purchases and they were both for over £3K... In South Africa!!!
The ironic thing is, my father had been in SA on business just before then, and his CC was automatically cancelled when he tried to use it there (he had never used it abroad before so the security algorithms kicked in and decided it had been cloned)
Luckily because it was a CC I didn't have to pay for it directly... but I (and all you other CC users) are now paying for it through a slight increase in rates due to the CC company losing money on it.