What a dork...
Almost falling for a scam like that, and admitting to it!
Is he a card-carrying member of the local 1D10T group?
US Banks.
I believe they don't use onetime pads or 'dohickeys' because they're too difficult for the average American to understand...
Of course, a lot of banks that DO use the 'dohickeys' implement the service incorrectly.
Usually, if it's the type where the code changes automatically, they define a 'bracketing' scheme, allowing the next or previous code to work instead of the 'correct' one(as defined by the server clock) to account for the cheap electronics, temperature variations and user fumbling.
Except...
Some banks set up a WIDE window, of maybe 5 or 7 allowed codes both ways.
This means that YOUR 'unique' code may be valid for 5 or 7 minutes(or more, if the clock in the dohickey is much off) where that one code is still valid and can be used to log in another session.
A GOOD bank setup is 1 or 2 minute brackets, then all transfers out of your accounts must be verified by a DIFFERENT code, and it must automatically disallow the code from being reused until the next time it cycles in naturally.
I know my bank follows the first two points. The third I haven't tested... yet...