function __callback(bytes32 _myid, string _result) {
        require(msg.sender == oraclize_cbAddress());

        address queryAddress = data.getAddressForQuery(_myid);
        bytes32 usernameAddress = data.getUserUsername(queryAddress);
        bytes32 resultBytes = stringToBytes32(_result);

        if (usernameAddress != resultBytes) {
            events.usernameDoesNotMatch(resultBytes, usernameAddress);
            return;
        }

        data.setVerified(queryAddress);
        data.setUsernameForAddress(usernameAddress, queryAddress);
        events.verifiedUser(usernameAddress);

        sendTip(usernameAddress, data.getBalanceForUser(usernameAddress));
    }