Double Spending

In a sentence

Consensus rules prevent a user from double spending the same coin in two transactions.

• Consensus rules prevent a user from double spending the same coin in two transactions.
• The merchant waited for confirmations to reduce the risk of a double-spending attempt.
• An attacker tried to reverse the first payment and spend the funds again.
• A successful 51% attack could enable some forms of double spending.
• The node rejected the later transaction because its input had already been spent.