That was Steam's fault for accepting unconfirmed transactions.
You can make a fake Bitcoin transaction but you can make 2 transactions using the same funds but going to different addresses. Only one of those will end up on the Blockchain. If steam waited for the transaction to appear on the Blockchain instead of just the mempool, they wouldn't have had the problem.
You can make a fake Bitcoin transaction but you can make 2 transactions using the same funds but going to different addresses. Only one of those will end up on the Blockchain. If steam waited for the transaction to appear on the Blockchain instead of just the mempool, they wouldn't have had the problem.