Probably explains...
...why my typical on-line transaction now goes something like....
<clickety click> Submit order
"Your card has been declined :("
<phone bank>
...time passes
...more time passes
...get to talk to someone with a heavy foreign accent. Give verbal DNA sample. Explain problem. Get transfered to fraud department.
...even more time passes
... get to talk to someone else with a different (but more local) foreign accent. Give verbal DNA sample. Explain problem again. Recite the last few transactions on the card. Blush. Get put on hold. Get told how wonderful their anti-fraud system is for blocking my unusual transaction (with a company I've only placed a few thousand pounds of order with over the last few years). Get told patronisingly that my card is now being unlocked and I can continue to use it in a few minutes time. Get asked if there is anything else they can help me with today. Resist making arrestable suggestion.
Wait a few minutes
Return to site
<clickety click> Submit order
"Your session has expired. For your security blah blah blah..."
Swear loudly
Re-enter order
Re-enter card details
<clickety click> Submit order
"Thank you for your custom...."
Swear mildly with relief, trying to think how to avoid this pantomime next time.