Wallpaper and Mold
Mold behind wallpaper is a big health concern. To get rid of the mold you must remove the wallpaper. First and foremost remove the wallpaper safely by wetting it with a wetting agent and water. But first wear a good cartridge-type respirator.
When removing mold behind wallpaper safely wet it first. Even if the wallpaper removes dry still wet it
A simple dust or particulate mask won't offer adequate protection. Also wear gloves and goggles, remember safety first. In a garden type sprayer add the wetting agent and water for easy application.
Using the sprayer to wet the wallpaper down will reduce the mold spores from becoming airborne. Even if the wallpaper removes dry still wet it first. Move slowly and deliberately so you don't stir up spores as you work.
Once the wallpaper is removed from the walls the next step is to wash the walls down with a water and bleach solution. This should remove the mold from the walls if it is just surface mold. If the walls are soft and spongy the mold may have penetrated deeper into the wall.
One way to tell if the walls are totally saturated with mold you can take a utility knife and cut a small square out of the wall and look at the back side of the square. If there is mold behind the wall then you should replace the walls. If you plan on wallpapering again use a Nonwoven wallpaper so you will never get mold behind wallpaper again. Nonwoven wallpapers can breath unlike vinyl wallpapers.