Another vector
Recently, Windows Update on my dad's laptop (this one, and his desktop PC are the only W7 systems in my care) b0rked. Several MSFT fixing tools chewed on the problem, but failed to correct it. So finally I put a new disk in, installed W7+SP1 (and Mint next to it), told it to fetch updates, AND VETTED THEM ONE BY ONE. All updates mentioned in one of the replies here or in the other W10 articles were unchecked and hidden, as well as any of the other updates that smelled even vaguely suspicious. The Do Not Want settings were applied to the registry, and only then were the remaining updates applied.
Still, powering up the lappie to hand it back last monday, it showed that &^%*&$^*^!! "Get W10" icon in the notification area. Investigating, it turned out that there were a couple of entries in the Task Scheduler related to GWX, which were terminated with extreme prejudice.
I ddin't have time to investigate the source of this particular GWX invasion, but told my dad not to click on it if it ever reappeared (he fully understands why, so I don't expect problems there) and let me know.
Arrgh.