Hack the Route Start free Open app Reconnaissance and exfiltration
OS fingerprinting
Guessing a machine's operating system from how its network code answers a few odd probes.
Every system's TCP/IP code answers slightly differently: the TTL it starts packets with, the window size it
offers, the TCP options and their order, how it treats a probe with strange flags. A scanner (nmap -O) sends a handful
of such probes and compares the answers with a database of known systems. The result is a near match, usually a range
of versions and sometimes more than one system: a guess, not a fact, and one a firewall or a tuned system can mislead.