If this is happening more than once then it sounds like your codebase is total shit (no offence) Hire an external auditor and have your code checked properly,

If this is happening more than once then it sounds like your codebase is total shit (no offence) Hire an external auditor and have your code checked properly, because it's only a matter of time before someone finds the 'big one' and that they won't tell you about.