Quote from: Jakesy on May 12, 2015, 03:32:07 PM

A confirmation is when a transaction exists in a block. Each subsequent block further confirms that transaction. 6 confirmations means that the transaction exists in a mined block and 5 other blocks were found thereafter. Remember, each block references the previous which makes this chain stronger. Its mathematically sound to allow for

A confirmed transaction is one in which the ENTIRE network has signed off on by including it in a block. 0 confirmations just means the transaction has been broadcast and miners should include it while trying to find the next block.

You can reverse a block with 25BTC worth of hashing power. That means each block costs around $6000 to reverse. You can't actually buy enough hashing power to do the reversal, but a rule of thumb would be that you need (value of item / $6000) in confirmations but at least 6 blocks to be very secure. For a "fighter jet" at $20 million, you would need 3-4 thousand blocks so that the value of the hashes securing the transaction was worth more than the transaction.