[lightedman]

I personally would have said to them "Would you like a fair trade? I've discovered a huge problem in your software that could allow anyone to remotely wipe their debt without you really knowing about it. I'll give that information in exchange for elimination of my debt. The money you'd lose from me is utterly dwarfed by the money you'd save by locking down this security issue, an issue which many bad actors would pay millions for. It makes financial sense and you'd be covering yourself security-wise. Win-win for all involved!"

[enriquto]

Sounds like you are threatening them. The idea is OK but the language should be much more subtle to be effective.