Ethereum Cookbook

How to do it…

1. It is not possible to fix the bug by updating the code in the smart contract due to the immutable nature of Ethereum smart contracts. Upgradable smart contracts are a way to overcome this issue for a certain limit. But, it reduces the user's trust in the smart contracts.
2. There are several design techniques that can be considered while writing smart contracts to minimize the effect of a potential bug.
3. Let's consider a simple contract that allows the deposit and withdrawal of Ether from a contract. We can try implementing various design techniques to avoid the loss of funds up to a certain limit:

pragma solidity ^0.4.24;contract VulnerableContract {    function deposit() public {        // Code to accept Ether    } function withdraw() public ...