As a site that runs advertising (on the "ad" side, which this post is) you likely see said advertisements; they're from Adsense, which is a Google property.
You might imagine that I frequently get solicitations from other ad networks that are not affiliated with Google trying to sell me on switching to their programs. I've checked a few out over the years and found them to either have ads that are ridiculously out of scope from reason (you know the type: "Doctors say do this NOW before you go to bed in order to .....") or are in some other ways inferior.
This site has a fairly strong TOS and privacy policy -- among them are that your login and other system-level data are off limits. That doesn't mean Adsense can't figure out who you are -- it probably can, but that's because there are tracking cookies all over the place and your browser "fingerprint" is by definition sent to every site you connect to -- which include all the ad requests your browser makes. This is inherently how the Internet works; even if you block all that the IP address from which the connection comes is inherently part of what the other end gets, and if its IPv6 it is likely globally unique to your device in some fashion. It also, of course, does not mean that if someone subpoenas me I won't provide the data -- of course I will, if a proper judicial request is made. But responding to a judge's order is rather different than selling you out for a few pennies to an advertising entity who, for all you know, is then going to sell that data to an insurance or other type of firm that will use it to screw you.
Recently I've started to get solicitations from various "newer" ad networks who want access to login specificity. Not your credentials, but enough to tie your ad experience directly to your signed-in status and, presumably, to you.
This is something that I explicitly state I will not do here -- my TOS explicitly states that any such advertising cookies an ad network generates and sends to you are outside of our control and we neither have them or interact with them. These folks want me to tie them to your account here via my explicit cooperation.
No, I won't do that -- but I'll bet other sites are and will, because if I'm being solicited by these guys so are others and you can bet some of them will bite on it in exchange for more ad revenue.
This is IMHO a serious problem and while it is not going on here because I won't participate in this sort of thing you can bet some other sites, if you have to sign into them, will do exactly that.