I had an interesting experience today when I tried to purchase some products on a website I hadnt purchased from before. As I went to the check out, I started typing my email address, this window popped up from shopify and asked if I wanted everything to be populated. I checked yes and I was shocked that all my contact and credit card information was populated.
The feature you're referring to here is known as Shopify Pay. This is a feature meant to accelerate the checkout process for customers. Once opted in, the credit card, shipping and billing information is stored securely and can be used across different shops to quickly move through the checkout. If you wish to opt out of this, you can scroll to the bottom of this page here to submit a request to have your information deleted.
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