[achivetta]

"Hi there, I was retyping a link to my invoice and screwed up a digit. It took to someone else's page, which seems odd. For example, my link was <link> and I accidentally typed <other link>. Not sure if this is a problem or anything, so I just wanted to bring it to your attention. I'm not sure if this is the right place to email, so please let me know that you get this."

When you make strong statements, other people often have a tendency to react strongly and defensively. I assume that the person at the other end is both competent and concerned - give them all benefits of the doubt.

If you find that isn't the case, then, and only then, you can email them and use the word "security" and talk about going public after n weeks, etc.

(I am not a lawyer.)