A LAN messenger is an instant messaging

Instant messaging

Instant Messaging is a form of real-time direct text-based chatting communication in push mode between two or more people using personal computers or other devices, along with shared clients. The user's text is conveyed over a network, such as the Internet...

 program designed for use within a single local area network

Local area network

A local area network is a computer network that interconnects computers in a limited area such as a home, school, computer laboratory, or office building...

 (LAN).

There are advantages using a LAN messenger over a normal instant messenger. The LAN messenger runs inside a company or private LAN, and so an active Internet connection or a central server

Server (computing)

In the context of client-server architecture, a server is a computer program running to serve the requests of other programs, the "clients". Thus, the "server" performs some computational task on behalf of "clients"...

 is not required (P2P

Peer-to-peer

Peer-to-peer computing or networking is a distributed application architecture that partitions tasks or workloads among peers. Peers are equally privileged, equipotent participants in the application...

). Only people who are inside the firewall

Firewall (computing)

A firewall is a device or set of devices designed to permit or deny network transmissions based upon a set of rules and is frequently used to protect networks from unauthorized access while permitting legitimate communications to pass....

 will have access to the system. Communication data does not leave the LAN, and also the system can not be spammed

Messaging spam

Messaging spam, sometimes called SPIM,is a type of spam targeting users of instant messaging services.-Instant messaging applications:...

 from the outside (Darknet).