Banner grabbing is the act of capturing the information provided by banners, configurable text-based welcome screens from network hosts that generally display system information. Banners are intended for network administration.
Banner grabbing is often used for white hat hacking endeavors like vulnerability analysis and penetration testing as well as gray hat activities (see: hacktivism) and black hat hacking. Banner screens can be accessed through Telnet at the command prompt on the target system’s IP address. Other tools for banner grabbing include Nmap, Netcat and SuperScan. A login screen, often associated with the banner, is intended for administrative use but can also provide access to a hacker. Meanwhile, the banner data can yield information about vulnerable software and services running on the host system.
For the sake of security, if banners are not a requirement of business or other software on a host system, the services that provide them may be disabled altogether. Banners can also be customized to present disinformation or even a warning message for hackers.