I've just had a look at the cookies on my machine (I use Opera - accept normal cookies without question, refuse all third-party cookies), and I do have the first cookie you mention, although not the other two. However, it's not a PPRuNe-only browser, and after deleting the cookie and setting Opera to prompt me about all cookies I'm not seeing it reset from PPRuNe when I log out and back in again (I've tried IE as well, same result)
I believe that PPRuNe customises advertising depending on your location - are you UK, or elsewhere?