Orchid scale is an annoying problem at best and a plant killer at worst. It can also be difficult to get rid of these pesky bugs once they infest a collection. I'll always try the following method first, before buying a powerful pesticide, which I don't like using indoors.
Use a Q-tip soaked in drugstore isopropyl alcohol and remove the bugs. Make sure to get under the leaves and down in the crease where the leaf joins the stem. Wipe the plant completely clean. After treating, spray thoroughly with a diluted alcohol solution. Repeat this treatment weekly until the infestation is under control.
And remember: keep your infested plants away from your healthy ones! You don't want to spread scale throughout all your orchids!