Re: 25% of people autofill credit card details?
"I always decline the kind offer for the browser to store the CC details."
Not to mention the websites who want to store your CC details.
"I assume that those who do autofill do not include the 3 digit security code"
Theoretically this shouldn't be stored either by the browser autofill nor by any of the websites that facilitate transactions (eg your Google account) nor the merchants' websites, but as you say, who knows? It's being sent on the form on every online transaction so in theory is available to store for all of the above.