This is happening as hackers unleashed a large distributed denial of service (DDoS) attack on the servers of Dyn, a major DNS host. It’s probably safe to assume that the two situations are related.
Domain Name Servers (DNS) act as the Internet’s phone book. Basically, they facilitate your request to go to a certain webpage and make sure you are taken to the right place.
If the DNS provider that handles requests for Twitter is down, well, good luck getting to Twitter. Some websites are coming back for some users, but it doesn’t look like the problem is fully resolved.
Below is a list of top website affected, some are back online.
Squarespace Customer Sites
Starbucks rewards/gift cards
Wix Customer Sites