What is the difference between TCP SYN and TCP SYN + ACK in a scan profile?

TCP SYN

The TCP SYN Ping sends a connection-like request to a port, receiving a reset (RST) for closed ports or an SYN/ACK for open ones. The scanner marks the host as responsive, regardless of port status.

TCP SYN + ACK

TCP ACK method sends an acknowledgment (ACK) for non-existent data, triggering an RST response revealing the host's presence. If no response is received back, the scanner will also try the TCP SYN method.

Both of those methods allow the scanner to navigate different firewall setups, increasing the chances of successful host discovery in diverse network environments.

An example case of where you might want to change this option is when assets are created even for non-responding IPs because of the firewall configuration.