Describe the security vulnerabilities exploited by the hackers?

'21st century bank heist' was one of the biggest bank robbery that was demonstrated by a group of hackers, and a global network of cyber criminals operating more than 26 countries stole 45 million by hacking into a database of prepaid debit cards. Hackers got into bank databases, and eliminated withdrawal limits on all available pre-paid debit cards and created access codes then loaded that data onto a plastic card (an old hotel's key card or expired credit card) with a magnetic stripe to that particular card and card now ready to work as long as the card carried the account data and correct access codes.

Prepared a network of operatives then blown out to rapidly withdraw money in multiple cities. The cells would take a cut...