>They know your domain, your IP address, [...] Yes, they can try to "fingerprint" your browser into a unique hash but that method is more reliable for desktops

>They know your domain, your IP address, [...] Yes, they can try to "fingerprint" your browser into a unique hash but that method is more reliable for desktops than mobile phones. Imagine a dozens of customers with identical iPhones sharing the wifi at Starbucks or the airport. (Everybody has the same ip address.) Sniffing for unique markers such as counting installed fonts and/or plugins isn't going to work on smartphones like it does on deskttops. Therefore, generating a cookie with an id is more reliable. Of course, people can negate that by configuring their phones to block cookies but it appears that most consumers don't do it (probably because it breaks other things such as banking, sports, etc websites.) Since advertising revenue from mobiles is growing faster than desktops, and in some cases exceeds it (Twitter mobile ads), it doesn't look like ad networks will favor fingerprinting over cookies. (That's not to say some sophisticated ad networks don't blend both techniques.)