<P> Banner grabbing is a technique used to glean information about a computer system on a network and the services running on its open ports . Administrators can use this to take inventory of the systems and services on their network . However, an intruder can use banner grabbing in order to find network hosts that are running versions of applications and operating systems with known exploits . </P> <P> Some examples of service ports used for banner grabbing are those used by Hyper Text Transfer Protocol (HTTP), File Transfer Protocol (FTP), and Simple Mail Transfer Protocol (SMTP); ports 80, 21, and 25 respectively . Tools commonly used to perform banner grabbing are Telnet, nmap, zmap and Netcat . </P>

In order to grab an os banner you would use