user14633: Is it possible to generate a key pair that has already been generated? Wouldn't it collide with an existing value? 
I assume it is mathematically very unlikely, but odds higher than 0 are still possible.

user15412: Yes, it is possible to create an already generated and in use address. The chances of that is indeed larger then 0, but minimalistic. But really small. And if I say really small, I mean extremely small. And if I say extremely small, I mean very extremely ultra low super duper close to zero. It is definitely NOT something to be considered as a weakness, never ever (because it will cost more energy before you have 50% to hit a duplicate address then the whole sun provides in its whole life time then). source  

14633: <p>Is it possible to generate a key pair that has already been generated? Wouldn't it collide with an existing value? </p>

<p>I assume it is mathematically very unlikely, but odds higher than 0 are still possible.</p>
 15412: <p>Yes, it is possible to create an already generated and in use address. The chances of that is indeed larger then 0, but minimalistic. But really small. And if I say really small, I mean extremely small. And if I say extremely small, I mean very extremely ultra low super duper close to zero. It is definitely <strong>NOT</strong> something to be considered as a weakness, never ever (because it will cost more energy before you have 50% to hit a duplicate address then the whole sun provides in its whole life time then). <a href="https://en.bitcoin.it/wiki/Weaknesses#Generating_tons_of_addresses" rel="nofollow">source </a> </p>
