Linden Lab have blogged an advisory informing people that they should update their Second Life payment info today. The advice is due to the fact that Linden Lab are transitioning to a new payment processor, as the blog post explains :
Second Life is transitioning to a new payments processor for credit cards. If you use a credit card for Second Life payments and have not added or updated your billing information since July 7, 2015, we strongly encourage you to re-enter your information to avoid any potential disruption of services. If you use PayPal or Skrill for Second Life payments, no action is needed.
The blog post explains how people can update their information, which generally is a pretty painless process.
A word of warning though, as Linden Lab are transitioning to a new payment processor, you may notice a small transaction is performed, Do not panic, these sort of confirmation charges are generally common these days for payment processors and any funds debited should be refunded quickly. The charges are generally of very small value, such as $1.00 or $2.00 and as I said, they get cancelled so the money is refunded to your account.
I have no idea who or what the new payments processor is, nor do I know who or what the old payments processor was, but there should be nothing to worry about here. However I would urge people to update their payment info as requested by Linden Lab, that should ensure there are no surprises about missed tier or premium membership payments.