NTLM, or New Technology LAN Manager, is a suite of authentication protocols that provides authentication, integrity, and confidentiality for users, particularly in Windows networked environments. Microsoft introduced NTLM with Windows NT to replace the older LAN Manager (LM) authentication protocol.
Despite its widespread use in older Windows systems, NTLM has been criticized for its security vulnerabilities. Microsoft has developed more secure authentication protocols like Kerberos, which is now the default protocol for Windows-based networks. NTLM is now used as a backup authentication protocol if Kerberos is not supported or configured.