Stripe records user movements on its customers' websites

Stripe cofounder here. The question raised ("Is Stripe collecting this data for advertising?") can be readily answered in the negative. This data has never been, would never be, and will never be sold/rented/etc. to advertisers.

Stripe.js collects this data only for fraud prevention -- it helps us detect bots who try to defraud businesses that use Stripe. (CAPTCHAs use similar techniques but result in more UI friction.) Stripe.js is part of the ML stack that helps us stop literally millions of fraudulent payments per day and techniques like this help us block fraud more effectively than almost anything else on the market. Businesses that use Stripe would lose a lot more money if it didn't exist. We see this directly: some businesses don't use Stripe.js and they are often suddenly and unpleasantly surprised when attacked by sophisticated fraud rings.

If you don't want to use Stripe.js, you definitely don't have to (or you can include it only on a minimal checkout page) -- it just depends how much PCI burden and fraud risk you'd like to take on.

We will immediately clarify the ToS language that makes this ambiguous. We'll also put up a clearer page about Stripe.js's fraud prevention.

(Updated to add: further down in this thread, fillskills writes[1]: "As someone who saw this first hand, Stripe’s fraud detection really works. Fraudulent transactions went down from ~2% to under 0.5% on hundreds of thousands of transactions per month. And it very likely saved our business at a very critical phase." This is what we're aiming for (and up against) with Stripe Radar and Stripe.js, and why we work on these technologies.)

[1] https://news.ycombinator.com/item?id=22938141

Stripe customer here. The question raised is, more broadly, "Is Stripe collecting this data in a legal and ethical way?" This too can be readily answered in the negative.

It doesn't matter whether "Stripe.js collects this data only for fraud prevention" or if it works in practice. Under CalOPPA [1], Stripe still has to disclose the collection of the data, and (among other things) allow customers to opt out of collection of this data, and allow customers to inspect the data collected. Stripe's privacy policy refers to opt-out and inspection rights about certain data, but AFAICT not this.

[This is not legal advice]

[1] http://leginfo.legislature.ca.gov/faces/codes_displayText.xh...

[2] https://stripe.com/privacy#your-rights-and-choices

From a legal perspective, isn't the burden of communicating privacy to the customer on the website/content provider, not Stripe?

Stripe.js is an API -- developers use this API to build something used by their customers. The customer is the one who's data is being collected, and the developers are the one's facilitating that collection via their service. The fact that it got sent to Stripe is not really relevant to who bears responsibility on clarifying data rights to the customer.