An ongoing DDoS attack is affecting several major websites including PayPal, making it difficult or impossible to connect to their website for checkout. This is also affecting other major sites that use Dyn DNS, and connection problems will likely continue until the attack is halted. Status updates from Dyn can be found here:
https://www.dynstatus.com/incidents/nlr4yrr162t8
Update: PayPal has finally sent out a notice of their own regarding the outage and should be emailing their users with details shortly:
PayPal Notify
Live Site Status Update
Notification: We are experiencing a system issue which may be affecting PayPal APIs and PayPal Website on the PayPal Live Site. We will send an update with additional details within the next 15-30 minutes.
Sent Oct 21, 2016 10:04 AM PDT by DBO
Start time: Oct 21, 2016 08:50 AM PDT
At this time, there is no alternative work-around.
Questions? Please contact PayPal Merchant Technical Services by filing a ticket; refer to PP-LIVE-7593
Update 2:
PayPal Notify
Live Site Status Update
Update 1: As a customer of Dyn Inc., PayPal is experiencing brief interruptions in service. This has prevented some of our customers from being able to pay with PayPal in certain regions. PayPal was not attacked directly, nor were any of our core services to business impacted in the disruption. We are sorry for the inconvenience, and remain committed to giving our customers around the world trusted and reliable ways to manage and move their money.
Sent Oct 21, 2016 01:01 PM MST by STC
Update 3: Dyn and PayPal both report that the attack was halted around 4pm MST.