Re: Another PS4 activated as primary - we only have one, so how do I fix it?

Well, in the end I decided to phone the UK Support.

To my surprise (after reading through this topic in it's entirity), they were EXTREMELEY helpful to my situation.

The explination I was provided was that I actually hadn't been compromised;  there is apparently a bug within the latest PS4 System Update which causes your existing PS4 to appear to be a different console, meaning it begins to think that another console is the primary (when it's not).

I'm not 100% convinced of this explaination, but he reset the activation for me over the phone and I was able to make my PS4 primary again during the phone call, so for me at least the problem was now resolved.

I would highly recommend calling them to see if you can get the same kind of results as I did.