Can you guys help me understand the math behind 6 confirmations? I have read that at 6 confirmations there is less than a 0.1% chance of a successful attack but I cannot remember where I read that. I have always wondered why the standard of waiting for confirmations to prevent a double spend attack was always 6 confirmations. I am aware that some places do allow at least 1 confirmation but if you accept 1 confirmation what percentage difference compared to 6 confirmations would I be taking a big risk by accepting 1 confirmations compared to 6?.
I'd say that it's fairly close to the figure
5 that is needed if we assume there is a miner or pool with 10% of the hashrate, so that's probably the assumption made when deciding for number 6, as well as it being easy to remember since 6 blocks in Bitcoin take exactly one hour on average.
That makes sense, because the largest pool (still F2Pool I believe) only has 13ish% of the total hashrate, so the advice of 6 confirms reflects the reality of the mining landscape.
It would be difficult, but not impossible, for an owner of multiple large pools to make them collude and thus require additional confirmations, but tensions inside the management resisting such an operation keep this a strictly theoretical scenario.