NTLM (NT LAN Manager) (not to be confused with LAN Manager) is a Microsoft authentication protocol. MS-CHAP is similar and is used for authentication with Microsoft remote access protocols. It is the successor of LANMAN (Microsoft LAN Manager), an older Microsoft authentication protocol, and attempted to be backwards compatible with LANMAN. NTLM was followed by NTLMv2, at which time the original was renamed to NTLMv1.