ChatGPT Tracks You Across the Web: How to Check and Block It
OpenAI's __obi cookie links your ChatGPT account to advertiser websites. Here is how the tracking SDK works, how to spot it, and how to protect your privacy.
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A cybersecurity report from Niebezpiecznik has exposed an advertising tracking mechanism run by OpenAI: on chatgpt.com, a unique identifier tied to your account is generated, stored in an __obi cookie under the .openai.com domain, and sent to websites run by companies buying ad inventory from ChatGPT. In practice, this means your conversations about sensitive health or financial questions and your online shopping activity can share an identical tracking anchor. You can verify this in your browser right now - and you should decide how to handle it.
What this actually means
The underlying tech is familiar - it relies on the same tracking pixels that online stores have placed for Meta and Google for years. What is new is the context it runs on. People share details in a chat prompt they would never post on social media: symptoms, debt, legal disputes. According to the investigation, OpenAI classifies __obi as an analytics cookie, which means it continues firing even if you reject marketing cookies in a site’s consent banner. This is critical: clicking “reject advertising cookies” may not stop this tracking chain at all.
The takeaway: if you turn to ChatGPT for sensitive matters, stop assuming the session is siloed from the rest of your web browsing. It is not that anyone is publishing your prompts, but your account identity and your browsing history are no longer kept in separate buckets.
How it works: three steps you can see for yourself
The technical investigation outlines a straightforward chain:
- On chatgpt.com, the platform generates an ID linked to your account and writes it into an
__obicookie on.openai.com, configured withSameSite=Noneand a one-year lifespan. TheSameSite=Noneflag is precisely what instructs your browser to attach the cookie to cross-site requests. - An advertiser embeds an OpenAI SDK script on their site, fetched directly from
bzrcdn.openai.com. - Your browser appends the
__obicookie to that script request the moment you load the advertiser’s page - before you even interact with the site.
Furthermore, the mechanism persists after logging out: the anonymous identifier is stable and stays unchanged for at least 27 days. Simply logging out of ChatGPT is not enough to clear the trail.
What the SDK collects across advertiser websites
According to the findings, the SDK harvests identity-matching data from form fields, on-page text, and the tag manager data layer (window.dataLayer). Email addresses and phone numbers are hashed using SHA-256. Country, region, city, and postal codes are transmitted in plain text.
Hashing an email address may sound secure, but in adtech it is the standard matching key: hashing the same email with the same algorithm always yields the exact same string, allowing ad platforms to join profiles across different databases. That is pseudonymization, not anonymization.
Among the URL paths observed during the research were pages covering medical conditions, debt settlement solutions, and a legal claim submission form. While OpenAI maintains an exclusion list for specific sensitive form inputs - such as passwords, payment cards, and medical histories - the URL string indicating the exact page you visited is not excluded.
The scope observed during testing covered 936 advertiser pixels spread across 1,029 domains, with Coursera identified among them. The researcher submitted detailed questions to OpenAI on September 14; customer support confirmed receipt, but the company provided no answers.
Your browser matters more than your chat settings
The technical breakdown was carried out on Google Chrome for Android. On iPhones, the mechanism fails to execute because all iOS browsers are required to use WebKit, which blocks third-party cookies by default. In this specific scenario, your operating system and browser engine provide stronger protection than any setting inside ChatGPT.
| Setup | Does the __obi mechanism work? | What this means for you |
|---|---|---|
| Chrome on Android | Yes - confirmed in testing | Manual intervention required: use blockers, separate profiles, or cookie controls |
| Any browser on iPhone (WebKit) | No - third-party cookies are blocked | You are excluded from this tracking chain by default |
| Chrome/Edge on desktop | Not determined in the original report | Verify manually using the steps below - do not assume |
| Firefox, Safari on desktop | Not determined in the original report | Both include built-in cookie isolation, but verify your setup |
To be clear: the source report did not include desktop test results, so we are not guessing what happens there without verification.
The GDPR issue: why cookie banners might not protect you
Under GDPR and similar privacy frameworks, non-essential cookies require explicit user consent. The problem lies in classification. If OpenAI categorizes __obi as an analytics cookie while the data feeds advertising attribution and identity matching, rejecting marketing cookies on a shopping site will not stop the browser from sending this cookie.
This is an editorial assessment based on the technical architecture, not an official regulatory determination. The report did not cite any formal enforcement action by data protection authorities, nor are we aware of any to date.
For website operators, there is also direct compliance liability: if you embed the OpenAI advertising SDK on your site, you are jointly responsible for the personal data transmitted from your forms and dataLayer. Auditing these scripts beforehand is essential.
How to check and protect your browser
- Check if the cookie exists. Open chatgpt.com, launch your browser’s Developer Tools (F12 on desktop), navigate to the Application or Storage tab, expand Cookies, and select
.openai.com. Look for__obi. Note its expiration date and the SameSite attribute. - Inspect third-party network traffic. In Developer Tools, open the Network tab, visit a major e-commerce or online education site, and filter network requests by
openaiandbzrcdn. If you spot a call tobzrcdn.openai.com, click on it and inspect the request headers to see ifCookie: __obiis included. - Review privacy and data controls in ChatGPT. Open your ChatGPT account Settings, head to the data and personalization controls, and opt out of advertising, personalization, and cross-activity tracking. Keep in mind that OpenAI updates setting names regularly, and the source report found no dedicated toggle for the
__obicookie itself, so treat this as risk reduction rather than an absolute fix. - Isolate ChatGPT from regular browsing. Run ChatGPT inside a dedicated browser profile or a sandboxed container. This is the single most reliable safeguard because it works regardless of how cookies are classified.
- Block third-party cookies. On Android Chrome, head to Settings, Privacy and security, Third-party cookies, and turn on blocking. You can also block
bzrcdn.openai.comat the DNS level or via content blocker rules, though newer ad domains may not yet appear in default filter lists. - Delete __obi and enforce cleanup. Clear stored cookies for
openai.comand configure your browser to wipe site data on exit. Remember that the anonymous identifier stays stable for 27 days, meaning a simple sign-out will not clear your footprint. - Segregate sensitive prompts. If you need to discuss medical symptoms, finances, or legal issues, use an isolated environment: a private window, a fresh browser profile, or a separate device entirely.
- If you manage a website: Audit all third-party scripts, check the contents of
window.dataLayer, and confirm that sensitive customer data, email addresses, and phone numbers are not exposed to third-party ad endpoints without explicit consent.
There is no single toggle that solves this. The most dependable defense is browser isolation: a dedicated profile for AI tools, strict third-party cookie blocking, and the awareness that signing out does not clear the tracking ID for nearly a month.
Source
Niebezpiecznik.pl: ChatGPT knows what you do in online stores and tracks your moves on other sites, September 21, 2026. Data regarding pixel counts, domains, cookie attributes, and the lack of response from OpenAI are drawn from this investigation. Prepared on October 8, 2026.
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