Updates with new clarifications from this comment:
Target Information
Kaspersky only saw evidence of victims IP addresses in Vietnam, El Salvador, Australia and the Philippines, and noted, “We observed three different infection chains overall, designed to attack about a dozen machines…”.
Thus, it wasn’t just “targeted” – out of all the update attempts that would have happened during the June to December timeframe, it appears there were only a dozen victims: everyone else got a normal, unaffected update, with no malicious payload.
Obvious Side-effect: Notepad++ Not Actually Updated after “Update”
When the attackers redirected victims, the victims got “updaters” which did nothing to notepad++.exe. If every time that automatic updates ran, you saw Notepad++ actually updated, you were not one of the victims.
In case the user runs Notepad++ updater, if the version remains exactly the same after the attempted update, the user can check %LOCALAPPDATA%\Notepad++\log\securityError.log to see what happened & report it.