These are the primary Windows Updates to avoid if you're not wanting to upgrade downgrade to Windows 10, or at least the ones I am aware of. Note that right-clicking and selecting 'hide' will not keep them out for good - Microsoft have managed to override your preferences and make these updates appear in Windows Update repeatedly, even after selecting 'hide'.

KB3035583 : the nagware in the task bar that started it all.

KB2952664 : re-introduced in Windows Update in January 2016, downloads the hidden W10 pre-installation file. This particular update was previously seen around June 2015. Keeps popping up again despite selecting to 'hide' the update.

KB3021917 : installs telemetry, last seen back in December 2014 and has not made an appearance since (that I'm aware of), but you can't trust Microsoft not to bring it back.
 
KB3123862 : introduced early February 2016, looks to be a new version of KB3035583 nagware. "The update adds capabilities to some computers that lets users easily learn about Windows 10 or start an upgrade to Windows 10." [more info].
 
I'm sure there will be more in time...

  

James_LI'll link the script to remove all current telemetry and suspect updates for Windows 7/8/8.1 to block them from being installed and remove those which are. It is located here in the middle of this particular script which will accomplish the task. Listed are the current KB updates which need to be avoided and removed if possible. I'm sure it will be updated as more information/KB articles are discovered.

 
I have been doing this through CMD but having a script to do it is a blessing.
 
Thanks for the link