"Hello, am I talking with Mr Smith?  My name's Rachel and I'm calling from the Internet Bank.  I need to discuss a small matter regarding your account, but first I need to take you through security if that's OK."

"Sure"

"Thank you.  Please could you confirm the first letter of your 7-letter password."

"P"

"Thank you.  And the 5th letter?"

"T"

"Thank you.  And finally the last letter?"

"L"

"Thank you, you're now through security...."