Unknown to many, Paypal provides no protection against fraudulent sales made with stolen credit card numbers when using their credit card payment option during a Paypal checkout (instead of logging into a paypal account).

To assist in minimising fraudulent sales you can switch off the ability to use Visa/Mastercard in a Paypal checkout, forcing shoppers to use a Paypal Account to pay.

The settings are well hidden.
Login to Paypal 

Go to : Profile (Cog next to Logout) 
Click : Selling Tools in left sidebar
Click : Website Preferences (Update) under My Business Set-up
Go to: Paypal Account Optional and change from On to Off.

Now no shopper can use a credit card to purchase, only a Paypal account.

Reverse this to change it back.