Microsoft has released numerous patches for its various operating systems, and it's difficult to keep track of what's been installed on a server, especially if you're not using some sort of patch management application.
Windows NT keeps track of this information in the following registry key:HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Hotfix
The Hotfix registry key has subkeys with names that correspond to the Microsoft Knowledge Base article in which the hot fix was released. For example, HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Hotfix\Q246009 is associated with the SP6a hot fix.
Inside the individual keys are values that provide information about the hot fix. However, not every key includes this information. Here's the information that's related to the SP6a hot fix:
"Installed"=dword:00000001 "Comments"="Windows NT 4.0 Hotfix: Service Pack 6 Re-release" "Backup Dir"="" "Fix Description"="Windows NT 4.0 Hotfix: Service Pack 6 Re-release" "Installed By"="" "Installed On"="" "Service Pack"=dword:00000006 "Valid"=dword:00000001