Invalidate LANMan

Two ways to stymie this poor security system.

One of the easiest holes to exploit in Windows Security is the LANManager security. LANManager is an incredibly weak security system that was used eons ago, back in the Windows for Workgroups (Windows 3.1) days. And of course, in the interests of backwards compatibility, it has lived on and on through each subsequent version of Windows. If you're interested in security, getting rid of older versions of Windows should really be a priority....

This tip contains two ways to prevent LANManager from coming back to haunt you, but they assume you don't have Windows NT or earlier systems in your environment.

First, use long passwords. The hash algorithm in LanManager only worked up to 14 characters, so passwords longer than 14 characters cannot be broken by the simple mechanisms routinely used to crack LanManager passwords.

Second, consider using Unicode in your password. It's fairly common for people to use punctuation marks and other non-standard characters from your keyboard in passwords to make them harder to guess, but Unicode passwords go an extra step, since LANManager doesn't do Unicode. However, they're a little harder to enter. Generally, you can hold the ALT key and type a 4-digit number from the keypad to enter Unicode characters. (Unicode characters are two-bytes and exist generally to support large alphabets.)


Thomas Alexander Lancaster IV is a consultant and author with over ten years experience in the networking industry, focused on Internet infrastructure.


This was first published in March 2003

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