I used to have an account with New England Merchants Bank. My ATM PIN was seven digits. But I noticed that the ATM screen would flash after the first four. A li

I used to have an account with New England Merchants Bank. My ATM PIN was seven digits. But I noticed that the ATM screen would flash after the first four. A little trial and error revealed that that was all I needed to enter! Comparing notes with friends (this was before the internet) revealed that this little secret was common knowledge. Subsequently, NEMB got subsumed by successively larger banks, until, finally, Bsnk of America took over. Suddenly, my ATM card wouldn't work! It turned out that they had kept my full PIN on file through the whole chain of acquisitions, but only with B of A did they start comparing ATM PIN entry against the full PIN! My card still worked with the full PIN (which I still remembered, it being an old phone number).