If you're super-technically adept, skip to the end to see the registry hack way of doing this directly.
Windows Update is generally useful. I like that it automatically patches my OS with all the latest security stuff. If you want to know why I like this please take a look at this article on herd immunity and then take a couple of minutes to think about it.
Anyway, the vexing thing is that at some time around 3am, when I am never there to tell it, "oh hell no, I have critical documents open!" Windows rolls an update and the computer helpfully restarts itself. Here's how to fix that little issue without turning off automatic updates in XP pro (for home edition you must hack the registry).
- Go to Start Menu -> Run type “gpedit.msc” and press Enter
- This opens the Group Policy editor
- In this window go to: Computer Configuration -> Administrative Template -> Windows Components -> Windows Update
- Double click on No auto-restart for scheduled Automatic Updates installations
- In the settings window Choose Enabled and click OK
- Close Group Policy Editor
The next time Windows Update updates your system it will not restart the computer automatically, but will notify you that restart is needed in order to finish the installation.
- Go to Start Menu -> Run type “regedit” and press Enter
- This opens the Registry Editor (if you are not sure of what you're doing STOP because you can completely hose your computer if you screw up)
- In this window go to: HKEY_LOCAL_MACHINE -> SOFTWARE -> Policies -> Microsoft -> Windows -> WindowsUpdate -> AU (if this key does not exist you must create it)
- Create a DWORD named NoAutoRebootWithLoggedOnUsers with a value of 1