Solidity : DoS with unexpected revert or failed call

External calls may fail to work accidentally or deliberately, which can cause a DoS state in the contract and enable an attacker to disrupt the logic of the contract, for example to unfairly win the auction.

To minimize the damage caused by such failures, it is better to isolate each external call into its own transaction that can be initiated by the recipient of the call. This is especially relevant for payments, where it is better to let users withdraw funds rather than push funds to them automatically.