Without having a picture I'd guess that they are probably copepods, amphipods, isopods, decapods, or any other manner of creepy crawly small crustacean... wikipedia just about any of those words and you'll find things that could pass for "small white bugs." If they are on your glass or substrate (not congregating on certain types of corals), they are all over the place, and you haven't noticed any problems with any tank inhabitants yet, then I would guess that they are good guys.