A question.
I understand ads on browsers that use cookies, but I don't understand how I get the same ad on a mobile app say instagram, for a search I did on laptop browser?

Thanks in advance.

this

I think collecting cookies is the personal they use to analyse your previous purchase history, any thing you search on Google search bar and so on with your same account logged in like of your gmail
So when the webpages apply for affiliation from companies like Amazon or Google, the companies make sure you are logged in through ur registered former account, they know their account history, that's how they do it I think

@sam9669

Exactly, the cookie identifies you on the device and if you at any time log into a service the cookie is bound to your google account or whichever it is.

Through the account they can track you between machines.

To day they can often do without the cookie using client fingerprinting.

This collects all info about the device that the browser displays which is a lot more than you might think.

Especially if they can use javascript.

One site that has tested this found that among 360 000 visitors 99% had a unique combination of versions and info.

This includes lang, timezone, browser string, plugins with versions (flash ...) and hardware info from 3D support like screen size, exact feature set and more.

Even private browsing does not protect completely from this.

@Voxera
1. Thanks for clarifying
2. So the devices are not safe itself ?
(I'm gonna wrap my phone in mylar)

@sam9669 and throw yourself in the sea...
This ia not as scary as you think it is. the scary part is that info is worth millions to someone. I'm pretty sure that the info is useless: most of us are into strange porn, pictures of cats, and stackoverflow.
What are they going to do with that combination?