OpenAI's ad collector at bzr.openai.com sets a cookie called __obi, scoped to .openai.com. The value is while you are on ChatGPT and tied to your ChatGPT account. __obi is then sent to OpenAI from ordinary websites you visit.
Any company that buys ads on ChatGPT installs
The internet was great until the pointy shoe brigade got too much power in tech companies.