I finally exposed my HW floors that have been covered with carpeting since
the 60's (not the same carpeting since then). The planks in the hallway are
loose and you can see them move when you walk on them. Either it was very
poorly done back then, or they came loose over time.

What's the best way to secure these? I don't have access from underneath.

I was thinking about drilling some 3/8" holes, screw them to joists, then
plug the holes with oak face grain plugs.

Anyone have a better idea?