Dear Ray,
First, thank you very much for your answer. Sounds scary :/
Well I have repoted it recently (maybe two weeks ago) and it had decent roots and new ones also. The pseudobulbs were like this since I have received the orchid in may 2015. And it has been blooming this will be third time already. I mist it every morning now with distilled water, but only slightly to wet the sphagnum moss which I have only on the surface of the pot. It is potted in the fresh Seramis orchid mix of bark and granulated clay.
In addition to my description of the problem and the orchid conditions I would add that by now these spots are not multiplying and that I have already sprayed it with 3% hydrogen peroxide soon as I saw it.... I hope I will save it...
J.