Disable auto-update in Notepad++

Simply go to:

Settings -> Preferences -> Misc -> and deselect "Enable Notepad++ auto-updater"

You may also be looking to turn off plugin update checking, in which case go to:

Plugins -> Plugin Manager -> Show Plugin Manager -> Settings (bottom left), and deselect "Notify of plugin updates at startup".

In newer versions of Notepad++ the option to disable automatic updating no longer appears in the Options dialog.

You can simply rename the C:\Program Files\Notepad++\updater directory to stop this feature. (e.g. rename it to updater_disabled)

Credit to http://wpkg.org/Notepad_plus_plus for suggesting the solution.