This spider is smaller than 1 mm and fast. The spider has tiny hairs on orange coloured legs. The backside of the spider is dark-brownish and has a small red stripe in the middle. I have taken pictures magnifying 25x using a lens of some watchmaker glasses. As a reference the lens of the lamp shining on the spider is 6mm. Found inside my house on the second floor on the attic.
I have searched all over the internet but I keep coming back to mites which this specimen doesn't resemble.
The spider skittered around again today and I managed to take a picture, unfortunately not a zoomed one but maybe some characteristics will be recognized.