[unishark]

It differs from blackmail because you the sick person are the one requiring others to perform a service for your benefit. With blackmail (and generally extortion) you are threatening to take an action unless someone pays you not to.

[phkahler]

Oh I completely agree, that's why I said "can also be like blackmail". Key word "like" because it does differ in the exact way you describe.

So in this threads context, "hey I found a vulnerability in your infrastructure, you could pay me for it" does not actually constitute blackmail unless they actually follow it with "I'm selling to the highest bidder which may not be you".