I don't know how this Strongbox works but I saw recently a new script which when there's any suspect access, it'll block the username until you change your username and password, and to do that you need to inform your last 4 digits of your credit card. I thought it was a good solution since it's not always the customer fault.
Maybe it's this Strongbox? I searched for its name on the error page but couldn't find ANYTHING related about it... I can just say it was being used on one of these sites:
http://www.dhdrevex.com/