> And perhaps a tool to e.g. do a checksum of all Notepad++ files, and compare them to the ones of a verified clean install of the user's installed version, would be a start?
Did I understand the attack wrongly? The software could have a 100% correct checksum, because the attack happened in a remote machine that deals with call home events from Notepad++, I guess one of those "Telemetry" add-ons. The attackers did a MITM to Notepad++ traffic.