[crsmith]

A couple of weeks ago I search for (on Google) and played (on YouTube, logged into my account) the Meow Mix song to play it for my 4 year old.

Less than an hour later, Instagram showed a Meow Mix advertisement on my wife's account, on her phone.

We have no animals. We have never had animals. She probably (though maybe not) has never logged into Instagram or Facebook on my browser.

It was too much of a coincidence.

[bigger_cheese]

I'm not surprised. Facebook track browsing habits use it to share advertisements with your friends.

I've shared this story on HN before this was what I experienced from 2016ish:

I saw an ad buried in my facebook feed to "buy Gallium and Bismuth metal in Australia" I thought it was an oddly specific ad so I made a joking post about it - turned out several of my friends were seeing the same ad. A common friend we all shared who is a high school science teacher spoke up. He explained his class was studying the periodic table and he had purchased samples of Bismuth and Gallium online to show to the class.

I'm absolutely convinced only reason my friends and I saw that ad was because we all shared a friend who was searching for this stuff online.

That level of surveillance is really creepy to me...

[ipython]

Definitely by IP address. I proxy all traffic for a family member in Central Europe and hilariously enough I get ads for “local” nightclubs that are thousands of miles away from me (east coast US).

What’s funnier is when google decides that it needs to localize my search results for that country. So there is a lot of tracking that assumes all traffic from a single residential IPv4 address is somehow correlated.

[1812Overture]

IP address, or if you have any shared accounts you could have a cookie identifying you as the same user. Ads also target connections of people who're interested in a product so you could get the ad from being friends/following someone who watched the videos. The ads will find you.

[crsmith]

Even if FB/Instagram knows my wife and I share an IP address or there were both FB/Instagram and Google cookies on the same browser where I searched for Meow Mix, how would Instagram know my Google/Youtube history?

[1812Overture]

That's easy. The ad network that serves you ads on YouTube also serves ads on Facebook. They have a profile of you that connects your facebook and google accounts.

[bluesign]

Probably tracked by your IP address.

[6ak74rfy]

I hate Facebook, but I don't think the example you gave is accurate. Both your searches would only be recorded by Google. And why would Google share any of it with Facebook?

The only way the data could have gone over is through a malicious browser extension.