The best way to tell if it is mold is to simply take a magnifying glass or loupe and get a close look at the white spots.

If it gllistens and/or looks likes a light dusting of powdered sugar, it's bloom and as the others have pointed out, that's a good thing. It's the oils of the tobacco crystalized on the wrapper surface.

If it's fuzzy or thread-like it's definitely mold. Mold can be white, green or blue among other colors but these three are the usual for tobacco.

If you determine that what you have is mold, be sure to inspect the foot (the end you light) of the cigar. If you see any mold there, chances are it has run through the cigar and you probably won't want to smoke it. If it's just on the surface of the wrapper, as CC pointed out, brush it off and light up!

One time I mailordered a box of Fonseca Cameroons only to be disappointed when I discovered that every one in the box was riddled with mold. Damned thing is, is that I was already half way down on one when I discovered the mold.