Network enumerating is a computing activity in which user names, and info on groups, shares and services of networked computers are retrieved. It should not be confused with Network mapping

Network Mapping

Network mapping is the study of the physical connectivity of networks. Internet mapping is the study of the physical connectivity of the Internet. Network mapping often attempts to determine the servers and operating systems run on networks...

 which only retrieves information about which servers are connected to a specific network and what operating system is run on them.

Software

A Network enumerator or network scanner is a computer program used to retrieve user names, and info on groups, shares and services of networked computers. This type of program scans network

Computer network

A computer network, often simply referred to as a network, is a collection of hardware components and computers interconnected by communication channels that allow sharing of resources and information....

s for vulnerabilities in the security of that network. If there is a vulnerability with the security of the network, it will send a report back to a hacker

Hacker (computer security)

In computer security and everyday language, a hacker is someone who breaks into computers and computer networks. Hackers may be motivated by a multitude of reasons, including profit, protest, or because of the challenge...

 who may use this info to exploit that network glitch to gain entry to the network or for other malicious activities. Ethical hackers often also use the information to remove the glitches and strengthen their network.

Malicious (or "black-hat") hackers can, on entry of the network, get to security sensitive information or corrupt the network making it useless. If this network belonged to a company which used this network on a regular basis, the company would lose the function to send information internally to other departments.

Network enumerators are often used by script kiddies for ease of use, as well as by more experienced hackers in cooperation with other programs/manual lookups. Also, whois

WHOIS

WHOIS is a query and response protocol that is widely used for querying databases that store the registered users or assignees of an Internet resource, such as a domain name, an IP address block, or an autonomous system, but is also used for a wider range of other information. The protocol stores...

 queries, zone transfers, ping sweep

Ping sweep

In computing, a ping sweep is a method that can establish a range of IP addresses which map to live hosts.The classic tool used for ping sweeps is , which traditionally was accompanied by gping to generate the list of hosts for large subnets, although more recent version of fping include that...

s and traceroute

Traceroute

traceroute is a computer network diagnostic tool for displaying the route and measuring transit delays of packets across an Internet Protocol network. Traceroute is available on most operating systems....

 can be performed.

Notable network enumerators

Notable enumerators are:

• Nmap
  Nmap
  Nmap is a security scanner originally written by Gordon Lyon used to discover hosts and services on a computer network, thus creating a "map" ofthe network...
  
  
• QualysGuard
• Nessus
  Nessus (software)
  In computer security, Nessus is a proprietary comprehensive vulnerability scanning program. It is free of charge for personal use in a non-enterprise environment. Its goal is to detect potential vulnerabilities on the tested systems. For example:...