How are sites like PayPal tracking me on other sites?

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I know cookies are a thing, but how do they know I’ve been on other sites? My reason for asking is that the last time I visited Groupon I received a coupon in my email for $5 off. Today I visited 1800flowers and got a PayPal coupon from them. I don’t have a PayPal app or anything, so how do they know I’ve been on groupon?

In: 0

any number of ways:
– tracking ids like Apple, Google Fb and pretty much every major service.
-ip address
-referring sites (you would be AMAZED to see how much detail your browser reports to sites, and what they’re able to process)
-nefarious usage of permissions (e.g. Amazon/Google constantly record/process almost all audio on your Mics, even when not in active use).

privacy on the internet is a myth

Those cookies are shared on services that feed PayPal, ebay, Amazon, google, Facebook, etc etc. While not all of those companies share the same singular service, the big ones, Amazon, google, Facebook, are enough of a coverage that your browsing activities are trackable

Ummm care to rephrase you case? Sounds like you got a coupon from Groupon and another one from 1800,. I don’t see what link you’re talking about. 800flowers sent you a Paypal coupon? Not a Groupon?

PayPal knows about your activity because the other sites you go to sell your traffic data in exchange for dollars. There are two possibilities – either 1-800-Flowers or Groupon have have a partnership directly with PayPal, or they sell their customer data. There are large exchanges where customer data is bought and sold to make advertising more effective.

In the first instance, Groupon might have a deal with PayPal where they send a web request to PayPal’s API whenever certain criteria are met. For example, they might see the PayPal cookie and then send a request to PayPal saying “Hey user 12345 in your system just logged onto our site and made this purchase.”

In the second instance, Groupon would sell a data set that says “This user made a purchase in our system, do with that knowledge what you will.” And then PayPal, and possibly others, would buy that data and consume it to make their own advertising decisions.

Source: I’m a software engineer that works in the advertising technology industry, although my company does not buy or sell any user data.