Just now, it was confirmed that "ChatGPT knows what you bought on other websites."
Yesterday, independent researcher Buchodi released a first-hand investigation that surged to 573 points and 308 comments on Hacker News.
He used his Android phone for an experiment, intercepting all the data quietly exchanged between the phone and various websites, then intercepted it again using a different method, confirming the results matched.
And it wasn’t just a day or two of observation. Buchodi monitored real browsing records for several months, covering nearly a thousand ad tracking points across thousands of websites.
The bottom line: Everything you searched for, viewed, or purchased on a merchant’s website can be traced back to your ChatGPT account through a single cookie.
This cookie is called __obi.
Three steps to get you connected
First, ChatGPT sends you a photo of an "ID expiring in 60 seconds."
The moment you open chatgpt.com, your browser generates a string of random numbers in the background and sends them to OpenAI's servers.
The server signs back a digital token, binding your ChatGPT account to this random number, which expires after 60 seconds.
Step two: This ID was exchanged for a Longevity Cookie.
The browser sends the token cross-site to bzr.openai.com, and the server responds by setting a __obi cookie under the .openai.com domain, valid for exactly one year.
The key is in the configuration: SameSite=None: This specifically allows the cookie to accompany cross-site requests. When you visit other websites, it goes with you.
In the same batch of requests, the browser blocked all other OpenAI cookies except for this one.
Step three: The merchant's website sends it back along the same path.
Companies that bought ads on ChatGPT install a small piece of OpenAI tracking code on their own websites—similar to Meta Pixel or Google Tag.
As soon as the code loads, __obi sends the page you're viewing, the product you're searching for, and your recent order back to OpenAI.
The most aggressive part is that the browser attaches the cookies to the script loading request before OpenAI’s code even runs.
The token has already been sent as soon as the page opened. You don’t need to click anything.
What you take back is finer than you think.
On Buchodi's own phone, the same __obi was sent from 12 commercial sites—including Chewy, Wayfair, HelloFresh, and Coursera—to OpenAI, and each time it was accepted normally.
When viewed over a longer time frame, it is common for the same user identifier to be repeatedly sent back to OpenAI by different merchant websites. In one case, a single user’s identifier appeared simultaneously in the return records of ten different merchants.
Not just the cookie itself.
This code from OpenAI can also actively extract information from the forms you're filling out and the text displayed on the page—even gathering more than what merchants voluntarily provide.
Your email, phone number, and name were encrypted before transmission, but your country, city, and postal code were sent in plain text. The postal code was the most heavily exploited field, harvested 100 times across 28 websites.
The URL you visited will also be sent back. Although the search terms have been removed, the page path remains.
Researchers found a page for checking diseases, a page for repayment plans, and a legal filing form in the collector's received paths.
Even more absurdly, the merchants themselves were also in the dark.
They simply installed a small piece of code at OpenAI’s request to track ad performance, completely unaware that their customers’ browsing records were being quietly linked to a ChatGPT account.
You think logging out of your ChatGPT account will get rid of it? Think again.
Researchers disassembled nearly a thousand identity credentials and found that even if you're not logged in, the system assigns your phone an anonymous identifier—one per device, lasting at least 27 days.
Logging out is just changing your disguise—the chase continues regardless.
Even more awkward is the label OpenAI applied to this cookie. In the privacy settings, “Analytics” and “Advertising & Marketing” are separate toggles—you can turn off advertising and marketing individually.
But __obi has been categorized under "Data Analysis".
In short: Even if you specifically go into your settings to disable ad tracking, this cookie will still be placed on your device.
On September 14, Buchodi sent two questions to OpenAI: Why is this considered analysis rather than marketing? And do people who opt out of marketing still get affected?
The customer service replied that they received it and will look into it internally. Neither of the two issues was addressed directly.
Not everyone was affected.
First, iPhone users can breathe a sigh of relief.
This entire mechanism only works on Android Chrome. Apple’s Safari inherently blocks such cross-site cookies, and the same applies to Chrome on iOS, so iPhone and iPad users are unaffected. Chrome on desktop has not yet been tested.
Secondly, this identifier is not triggered every time you open ChatGPT—it appears roughly once in every five sessions, and it doesn’t trigger at all on the mobile web version.
The most crucial point Buchodi also wrote: he can only prove that the data was sent to OpenAI’s servers, but he doesn’t know whether OpenAI actually matched it to your account.
After all, he didn’t see firsthand how the server processes it.
Old technology, new place
However, to be fair, this approach was not invented by OpenAI.
Facebook has been doing this for years. While you’re on Facebook and browsing other shopping websites, those sites send your browsing data back to Facebook through Facebook’s tracking code, allowing Facebook to know what you’ve viewed and purchased.
We've been doing this in the advertising industry for over a decade.
In February this year, ChatGPT officially began selling ad space, and by the end of April, marketing tracking was enabled by default for free users.
At the time, people were concerned about data leaking out of ChatGPT.
Today’s survey reveals the opposite—your browsing history outside is converging on your ChatGPT account.
What people say to ChatGPT are often things they wouldn't post on their social media feed.
And now, ChatGPT is increasingly placing orders, booking tickets, and handling tasks for you.
Advertising technology is old. What’s new is that what you’ve told AI and what you’ve purchased elsewhere are now being linked to a single account.
Reference: https://www.buchodi.com/chatgpt-now-knows-what-you-do-on-other-websites-via-ad-collector
This article is from the WeChat public account "New Intelligence Yuan," authored by ASI Revelation, edited by Solomon.