How Does a Transaction’s Confirmation Status Relate to Double-Spending Risk?

The risk of a transaction being reversed (double-spent) decreases significantly with each block confirmation it receives. A zero-confirmation transaction has the highest risk.

Once a transaction is included in a block and that block is followed by subsequent blocks (confirmations), the cost for an attacker to re-mine the chain and reverse the transaction becomes exponentially higher, effectively making the transaction more secure and final.