Chocolate develops the white surface for three reasons: one is from heat. The heat drives fat out of the chocolate and it makes a white coat on the surface. The second is from cold. When chocolate gets cold and is placed in a warm area (where the chocolate is colder then the air's dew point) moisture condenses on the surface. The water draws sugar out of the chocolate and makes a white coating. Both conditions are called "bloom." The last reason is from scuffing. When chocolate chips (for example) tumble on conveyor belts, they can become scuffed which looks white. To tell the difference, look in the curl of the choc chip. If it is shiny, the problem is scuffing, if not, it is bloomed.
Bloom changes the eating characteristics of the choc. If you are baking, it should be just fine... I make cookies with bloomed chips and they are fine. Eating out of hand, bloomed chocolate isn't very good. I'd recommend melting it in a double boiler using it to make your own chocolate drops or bars.
If the chocolate is a filled bar, it probably won't taste very good. It will be safe to eat though.
Answer provided by eccevita on Yahoo Answers Canada