Withering cyberattacks on server farms of a key Internet firm repeatedly disrupted access to major websites and online services including Twitter, Netflix and PayPal across the U.S. on Friday. The White House called the disruption malicious and a hacker group claimed responsibility, though its assertion couldn’t be verified.

Manchester, N.H.-based Dyn said its data centers were hit by three waves of distributed denial-of-service attacks, which overwhelm targeted machines with junk data traffic. The attacks, shifting geographically, had knock-on effects for users trying to access popular websites across the U.S. even in Europe.

“The complexity of the attacks is what is making it so difficult for us,” said Kyle York, the company’s chief strategy officer. “What they are actually doing is moving around the world with each attack.” He said an East Coast data center was hit first; attacks on an offshore target followed later.

The data flood came from tens of millions of different Internet-connected machines — including increasingly popular but highly insecure household devices such as web-connected cameras. It was an onslaught whose global shifts suggested a sophisticated attacker, though Dyn said it had neither suspect nor motive.

The level of disruption was difficult to gauge, but Dyn serves some of the biggest names on the Web, providing the domain name services that translate the numerical Internet addresses into human-readable destinations such as “twitter.com.”