Nmap ("Network Mapper") is a free and open source utility for network exploration or security auditing.

Version 5.00 is the first major release since 4.50 in 2007, and includes about 600 changes.

Top 5 improvements in Nmap 5:

• The new Ncat tool aims to be a Swiss Army Knife for data transfer, redirection, and debugging
• Ndiff makes it easy to automatically scan your network daily and report on any changes (systems coming up or going down or changes to the software services they are running). The other two tools now packaged with Nmap itself are Ncat and the improved Zenmap GUI and results viewer
• Improved Nmap performance allows Nmap to scan fewer ports by default while finding more open ports. Also added is a fixed-rate scan engine so you can bypass Nmap's congestion control algorithms and scan at exactly the rate (packets per second) you specify
• Nmap Network Scanning, the official Nmap guide to network discovery and security scanning, has been released. From explaining port scanning basics for novices to detailing low-level packet crafting methods used by advanced hackers, this book suits all levels of security and networking professionals. A 42-page reference guide documents every Nmap feature and option, while the rest of the book demonstrates how to apply those features to quickly solve real-world tasks
• The Nmap Scripting Engine allows users to write (and share) simple scripts to automate a wide variety of networking tasks. All existing scripts have been improved, and 32 new ones added. New scripts include a lot of MSRPC/NetBIOS attacks, queries, and vulnerability probes; open proxy detection; whois and AS number lookup queries; brute force attack scripts against the SNMP and POP3 protocols; and many more.