Rejoice! To find white powdery spots is a good sign that your cigars are aging beautifully. The appearance of these white spots, called bloom or plume, means that the essential oils contained in the tobacco have come to the surface of the cigar. They are easily brushed off.
However, if the spots are blue/green, fuzzy and leave a stain when you brush them off, the spots are probably mold. Mold is a damaging fungus that results from storing cigars in too high humidity and will ruin the taste of your cigars. In this case, separate the affected cigars from the others and clean your humidor. Leave your cigars outside the humidor for a few days until you are sure that the mold growth has stopped. It is important to bring down the humidity inside the humidor before placing the cigars in it again.
If the mold appears to be just on the surface of the wrapper and has not spread to the interior, the taste may not be affected.