try this, take a magnet in your hand and slowly move it towards the screen. youll notice the screen changes colors. if you get too close with it youll make the color change stay for a long time. like a few weeks.
if you are absolutally worried about your hard drives, just glue a ferrite to the back of the magnet.
ferrites absorb magnetic fields.
or just put a peice of iron or steel between them and the magnets. it condenses the magnetic field and as long as it does not saturate, the iron will keep the fiel from reaching the hdds and make the field on the other side strong. this is called adding external iron.