Nmap Abbreviated as Network Mapper, Nmap Security scanner is a free, open source utility used for security auditing and network exploration. It is found useful by numerous network and systems administrators for a wide variety of tasks such as network inventory, monitoring host/service uptime and managing service upgrade schedules.
Raw IP packets are used in unique ways in order to determine the hosts that are available on the network and the kind of services (application name and version) that are being offered by those hosts, the kind of operating systems are being run by them, the type of packet filters/firewalls currently in use and various other characteristics. It was especially designed for rapid scanning of large networks, while it is also meant for single hosts.
Being readily available for a plethora of operating system platforms Nmap’s standard download includes a compressed file that contains the UNIX version (running on Linux, Free/Net/OpenBSD, Solaris and Mac OS X), the Windows version as well as the X-Windows front end for UNIX (NmapFE), and the recommended Windows GUI for Nmap (NmapWIN).
A wide variety of scans can be performed by Nmap, some being aggressive, while some are designed for stealthy and undetected scans. One can discover different information, depending on the scan type that is performed.