Hack the Route Start free Open app Reconnaissance and exfiltration
Half-open scan
Probing a TCP port with a SYN and hanging up after the reply, so no connection is ever made.
A scanner sends a SYN; an open port answers SYN/ACK, a closed one a reset. Instead of the ACK that would finish the
handshake, the scanner sends a reset, so the service behind the port never gets a connection and never logs one
(nmap -sS, which needs root to send its own packets). A connect scan (nmap -sT) makes the full connection
through the system, as any program does, and shows up in the service's log. Half-open is quieter, not invisible: the
packets still cross the wire.