Which part of the UDP header would attackers replace if they change the data payload to prevent the receiver from identifying the change?

If attackers change the data payload in a UDP (User Datagram Protocol) packet and want to prevent the receiver from identifying the change, they would need to alter the UDP checksum. The UDP checksum is a field in the UDP header that provides a basic level of integrity checking. If the data payload is altered, the checksum would need to be recalculated and replaced in the packet to match the altered data. If not done correctly, the receiver would notice a mismatch between the expected checksum and the checksum of the received packet, indicating that the data has been tampered with.