When the flow of control is transferred to an external contract, the execution of the caller contract can fail accidentally or deliberately, which can cause a DoS state in the caller contract. The caller contract can be in a DoS state when a transaction is reverted due to a failure in an external call, or the callee contract deliberately causes the transaction to be reverted to disrupt the execution of the caller contract. Scan your smart contracts using Smart Scan Tool to detect DOS due to Unexpected Revert Vulnerability in Ethereum Smart Contracts.