does a screen capture show the squares? try to get them to appear, and when they do hold power and volume down...the screen capture will appear in the gallery.
in my backwords thinking...a screencapture would capture anything going on with the system and would NOT capture phisical screen defects or manufacturer defects.
so if the screen cap shows the squares, it is a software issue and a factory data reset should correct the problem (it was probably one of the apps you just updated) if it does not show the problem, it is probably a hardware issue.
either way, it is not normal and should be fixed quickly. neither one is something to be overlooked b/c a hardware issue will only get worse, and an OS issue will also, only get worse.