Enabling NTLMv2 on Windows XP Home Computers

Please note: These instructions are based on a computer running the latest service pack, Windows XP Service Pack 2. This software can be downloaded directly from Microsoft's Website.

In order to enable NTLMv2 on a Windows XP Home computer, you will need to make a few changes to the Registry.

Warning: Before you attempt to make any changes to the registry, please back it up and make sure you know how to restore if there is a problem afterward. See Microsoft's Knowledge Base article - 322756 - How to back up, edit, and restore the registry in Windows XP and Windows Server 2003.

  1. Select the "Start Menu" and then select "Run...".

  2. In the "Run..." dialog box, type regedt32, then click the OK button to open the Registry Editor.

  3. In the left hand window, expand "HKEY_LOCAL_MACHINE".

  4. In the left hand window, expand "SYSTEM".

  5. In the left hand window, expand "CurrentControlSet".

  6. In the left hand window, expand "Control".

  7. In the left hand window, expand "Lsa".

  8. In the right hand window, double-click the "lmcompatibilitylevel" setting.

  9. You will be presented with the "Edit DWORD Value" dialog box.

  10. In the Edit DWORD Value dialog box, change the Value data: text from "0" to "5", make sure that "Hexadecimal" radio button is chosen for the Base section, and then click the OK button

  11. In the right hand window, the "lmcompatibilitylevel" setting should reflect the new setting change.

  12. Please restart your computer.

Please Note: By following the instructions in these guides, you will be changing your Windows clients to only use NTLMv2 authentication and refuse everything else. In changing to this highest level of security, you may have difficulty connecting to other Windows machines that have not had the equivalent change made. If you regularly connect to other Windows systems you should either follow the instructions to enable NTLMv2 on them too (where possible) or, alternatively, experiment with a lower setting of the LAN Manager Authentication Level. Due to the insecurity of the LM hash in particular, IMSS strongly recommends enabling NTLMv2 on each of your Windows machines or, failing that, choosing the highest LAN Manager Authentication level possible.