I remember a few years back they were (or claimed to be) under a yuuuge DDoS attack. They then said they had made a partnership with a security firm and that fixed the problem. When I looked up that company, I remember coming to the conclusion that it was linked to Mossad.

Proton are also people from CERN. I remember reading quite a few disturbing things about that group.

I still use the service for certain things, but I'm under no illusion as to what I'm getting.