I discovered why. Technical details here http://aka.ms/sha1
Non-technical summary: MS decided to not trust an algorithm on a purely theoretical weakness (which I find a bit hilarious... we're signing games, not top secret software!!) and so marked as invalid all the installers I did.
Of course if you just use Chrome or Firefox (as I do) you won't see any message

But in practice it means I need to rebuild/resign/reinstall ALL the Windows installers!


For now I'll wait, because I was planning to do that already but when Ren'Py reached the new stable release (since also fixes some other issues). In any case even if you see those warnings, my games works just fine and aren't a threat to the world security
