Third-party cookies are set in your pc from domains aside from the one that you simply’re really on proper now. For instance, if I log into css-tricks.com, I will get a cookie from css-tricks.com that handles my authentication. However css-tricks.com may additionally load a picture from another website. A typical tactic in internet marketing is to render a “monitoring pixel” picture (effectively named, proper?) that’s used to trace promoting impressions. That request to a different website for the picture (say, advert.doubleclick.com) can also set a cookie.
Eric Lawrence explains the difficulty:
The monitoring pixel’s cookie is named a 3rd occasion cookie as a result of it was set by a site unrelated to the web page itself.
In the event you later go to B.textslashplain.com, which additionally comprises a monitoring pixel from advert.doubleclick.web, the monitoring pixel’s cookie set in your go to to A.instance.com is shipped to advert.doubleclick.web, and now that tracker is aware of that you simply’ve visited each websites. As you browse increasingly websites that comprise a monitoring pixel from the identical supplier, that supplier can construct up a really full profile of the websites you want to go to, and use that info to focus on advertisements to you, promote the info to a knowledge aggregation firm, and so on.
However occasions are a changin’. Eric goes on to elucidate the browser panorama:
The default stuff is the massive deal, as a result of all browsers provide some option to block third-party cookies. However after all, no person really does it. Jeremy:
It’s exhausting to imagine that we ever allowed third-party cookies and scripts within the first place. Between them, they’re chargeable for the worst ills of the World Extensive Net.
2019 is the 12 months we apparently reached the breaking level.