[manigandham]

There are lots of ways data is shared.

For the vast majority, it's demographics and interest based stuff. LinkedIn for example will keep lots of 1st party data to itself for it's own ad business but will share generic data like: female, 30s, IT engineer, new york, etc. This is how much of the ad targeting works. Trying to target a single person/identity just isn't easy, scalable or worth it so big overlapping buckets are used.

On the other side, specific identity data is also shared, called PII (personally identifying information), in a hashed format with other data networks. This is often used in retargeting by profile, an example being if a company wants to target all of it's current customers, it'll upload it's CRM database full of emails and data providers will match this up to cookies or other identifiers and let that company target these users with ads online. It's anonymized in that the advertising company doesnt know your identity, just that you're in this bucket of "XYZ email address list".

The way providers get to know your identity is major sites that share your profile data when you login, because they definitely know that it's you. LinkedIn will set a cookie when you login and then they'll have an API or data dump to other providers that can request your info or if you fit a bucket (in a hashed format).

Data is usually on a CPM (cost per 1000 impressions) basis although ranges widely from $1-$100 depending on quality and depth of targeting.

[annnnd]

Thanks for info, didn't know that! If I understand correctly, you don't get the data about specific users, like OP did?

About me being downvoted - yeah, I figured I would be, because lots of people here use voting as "I (dis)agree" or "I (don't) like" button instead of "post is (not) useful" button. For the record: I would rather live in a world where such tracking was not possible and/or allowed, however, this is just not the case. As business you would be stupid to not consider using such data though. I personally would welcome a browser with privacy built in (for instance, browser which would disallowed all references to external domains - including images, JS and similar). But in reality this probably wouldn't fly.

[manigandham]

Advertisers don't. It's all anonymized and usually as a big bucket of either demographics, interests or matched to a customer list of some sort. Honestly targeting an individual person online is very hard and expensive - at that point you probably have their name so you can just get their address and send them some mail instead.

The major companies like Google, Facebook, LinkedIn and other sites with logins will have more personal info because people provide it willingly, but they also keep this as valuable 1st party data since it's their edge in the ad business. Advertisers don't get access to it but can target against it if they advertiser on that specific platform.