If for some reason you just have to keep running a Windows XP machine and would like to continue receiving at least some patches and updates;
I have an old server at home that I use for FTP and VOIP still running XP. I wasn’t thrilled about spending money on it to upgrade the OS but I didn’t want it to run completely un-patched either.
I’ve used this trick on that machine and can confirm that it works as intended without any negative results.
Create a text file using notepad and give the file a .reg extension
Use the contents below in the text file:
Windows Registry Editor Version 5.00
Save the file
Double click on the file from the saved location
When asked if you want to save changes to the registry select yes
Run Windows Update
If you are running Microsoft Security Essentials you will still get a red flag notification about Operating System Support has ended. If you don't want to see the notification you can click to close out of it or alternatively use another AV solution.