Networking problems after the October 2026 Windows update? NTLM might be to blame

The October 2026 Windows security update may break networking for some customers who are still clinging to long-deprecated NTLMv1 security. A seemingly minor change in the update could have major implications for administrators and enterprises that haven't fully moved away from the legacy technology. Before the October 2026 update, Windows permitted NTLMv1-derived credentials for Single Sign-On and generated warning events. After the update, requests to use NTLMv1-derived credentials are blocked