Henry Is a cyber security specialist hired by BlackEye - Cyber security solutions. He was tasked with discovering the operating system (OS) of a host. He used the Unkornscan tool to discover the OS of

A TTL of 64 is the default value used by Linux and Unix-based operating systems such as Debian, Ubuntu, and macOS, not Windows.

Windows operating systems set a default TTL of 128 in outgoing IP packets, which is a well-documented fingerprinting signature used by tools such as Unicornscan and Nmap. When a probe response returns with a TTL value at or near 128, it reliably indicates the target is running a Windows-based operating system, distinguishing it from Linux systems (TTL 64) and network infrastructure devices (TTL 255).

A TTL of 255 is the default for network infrastructure devices such as Cisco routers and switches, as well as some Unix variants like Solaris and AIX, not Windows systems.

138 is not a standard default TTL value for any major operating system; OS vendors configure default TTL at fixed values of 64, 128, or 255.