My credit card I had linked to my PayPal account was recently about to expire. Therefore, I went in and updated my information, which in this case was simply changing the expiration date on the Mastercard.
I noticed on my bank statement that I was charged a $1.00 fee from PayPal, however there were no details. Usually, when authorizing a credit card with PayPal they notify you that there will be a small charge, accompanied by a 4 digit number to confirm. This allows you to prove that the card is in fact yours. I was not notified of a charge, nor where there any codes to enter into PayPal or attached to the transaction.