Information
LAN Manager (LM) is a family of early Microsoft client/server software that allows users to link personal computers together on a single network. The default setting on servers allows all clients to authenticate with servers and use their resources. However, this means that LM responses -- the weakest form of authentication response -- are sent over the network, and it is potentially possible for attackers to sniff that traffic to more easily reproduce the user's password.
Solution
Make sure 'Network security: LAN Manager authentication level' is set to send NTLMv2 response only and refuse LM and NTLM.