An issue was discovered in a smart contract implementation for UserWallet 0x0a7bca9FB7AfF26c6ED8029BB6f0F5D291587c42, an Ethereum token. First, suppose that the owner adds the evil contract address to his sweepers. The evil contract looks like this: contract Exploit { uint public start; function sweep(address _token, uint _amount) returns (bool) { start = 0x123456789; return true;} }. Then, when one calls the function sweep() in the UserWallet contract, it will change the sweeperList to 0X123456789.