Analysts and company officials are blaming a cyberattack on a key Internet routing firm for disruptions to popular websites across the US, Canada and Europe.
The White House is calling the activity malicious.
New Hampshire-based Dyn Inc. says its server infrastructure was hit by distributed denial-of-service attacks, which work by overwhelming targeted machines with junk data traffic.
The Twitter, Netflix and PayPal websites were among those affected by the hacks.
Members of a shadowy collective spread across China and Russia that calls itself New World Hackers claimed responsibility for the attack via Twitter.
They said they organized networks of connected "zombie" computers called botnets that threw a staggering 1.2 terabits per second of data at the Dyn-managed servers.