How is it possible, incorrect keyboard assignments I've been having a strange problem and I would like to know from someone from a programming point of view, how this is possible. 

Let me explain, I have been using Blender for a while when all of sudden my keyboard hotkeys changed their assigned function. For instance, in the edit mode box select, shift b went from selecting to changing the view and when I selected an object to add a modifier to the modifier was assigned to all the visible objects in the scene and were many more.

How are keyboard letters assigned their function and how could they change what they were assigned to do? 

One other thing I did to try and fix this problem was I deleted Blender and reinstalled a fresh copy. The strange thing was that the new copy of Blender kept the same incorrect functions as the old copy.

I am using Blender 2.79 running on a windows 10 computer.
Do you have multiple languages on your computer?  I ran into this b/c I also have French on my computer and whenever I pressed alt+something (I never figured out what I pressed) it would change languages and so the keyboard would change and so would the shortcuts.  The way to fix this is to minimize Blender, go on the taskbar, bottom right, and see if there is a different language select.  If so, you've found your problem, just click on it and change it back.  If not, IDK.