Newcastle Building Society Fail
"The Newcastle" asks for a memorable date. Now most people will choose a date of birth or marriage, etc. of a relative or friend.
Say 8th June 1950 (08061950)
Then they ask for three digits from that date:
Digit 3 - can only be zero or one
Digit 5 - for the last millennium or so at least, 1 or 2
Digit 1 - can only be 0,1,2 or 3
That means I have approximately 1 in 16 chance of a completely (well, almost) random guess being correct.
Also for dates in the recent past, digit 6 is likely to be either 9 or 0.
I told them about this years ago - did they change it? of course not.