Cleaning up my mailbox, I have discovered fascinating thread on credit card security at UKCrypto. A teaser: 

"The UK model makes use of a financial parameter called the "floor limit". The norm is that all transactions below the floor limit are offline and the transaction record is stored locally until collected by an organisation known as an "acquirer". Above the floor limit, an online check and reservation of value takes place first. In addition, there are other rules, such as a requirement for a certain but small percentage of transactions to be chosen at random for online verification. And there is a card blacklist downloaded into the terminal.

This model grew up because of the very high cost of telephone calls. Instead, the accumulated transaction records were collected overnight by phone - and this still happens for many small merchants."

8:01:18 PM