I can update this observation. ProSoft Engineering has inserted a cookie a couple of times without my going to their site - and it wasn't a plain-Jane cookie, it was a tracking cookie.
And, I can update the update. I've taken advantage of the Cookie Window, which allows real-time observation of cookies being installed and whether they are tracking cookies. The Prosoft Engineering cookie, which continues to pop up periodically,
does not require Safari to be open. The Prosoft cookie will appear as soon as the computer is booted.
Now,
that's persistent!
Maybe ask Russell about it? He's both responsive and helpful.
I haven't contacted the publisher yet.
