NTLMV, or NT LAN Manager Version, is a Microsoft authentication protocol used in network environments to provide secure authentication for users and services. It is part of the NTLM authentication suite, which is primarily used in Windows operating systems. NTLMV is considered less secure than more modern protocols like Kerberos, as it is vulnerable to various types of attacks, including pass-the-hash attacks. Despite its limitations, NTLMV is still used in legacy systems for compatibility purposes.