NT LAN Manager

A Microsoft IIS web server integrated authentication method.

(Also known as Windows NT Challenge/Response authentication; recently updated and renamed Integrated Windows Authentication) NTLM is a Microsoft IIS (Internet Information Services) integrated authentication method. NTLM is used by such Microsoft applications as Active Directory and Sharepoint.

Note that NTLM has the following restriction: NTLM can get past a firewall, but is generally stopped by proxies because NTLM is connection-based, and proxies do not necessarily keep connections established. Applications such as Sharepoint inside an enterprise that require Integrated Windows Authentication (which includes NTLM authentication and Kerberos v5 authentication) should add the local IP address of servers hosting these applications to the browser’s proxy exemption list.