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?.
2 confirmations is more than enough for the bitcoin network, unless you are talking about millions of dollars.
When you make a transaction, that transaction is recorded in the blockchain. Each subsequent block that is mined adds one more confirmation to that transaction.
A successful attacker will need to mine all blocks again since your transaction. It is considered permanent and practically impossible for an attacker to mine 6 blocks faster than the whole network. This is why 6 confirmations is enough.
If you are talking about altcoins, like bch or brg which have significant lower hashrate, the 6 confirmation rule is not enough.