I just got an answer to one of my question that sent me refresh my memory about Vernon Vinge’s “Zones of Thought” Universe. There I saw the word “Blight”, and this reminded me of something which might have deserved that name. But it is not it at all a “malevolent super-intelligent entity”, as Vinge's Blight, but a kind of infection.
It is some kind of weird illness that makes people and machines blend into each other. I remember in particular a very striking case of the captain of a spaceship whose head and torso were still human, but whose legs had become huge, metallic, essentially a part of his ship. His case was a bit extreme, but it was by no means unique, the “illness” was quite extensive. And IIRC, it is mentioned in several books in a series.
Ideally, I’d like to find the book with this unfortunate captain. But just the name of the series would be enough. I guess I could try book after book till I find the right one.
I read it about 10-15 years ago. I think it was pretty recent then, but I could be wrong, it might be much earlier, but it does not "feel" like an "old classic"..