Why Twitter, Spotify and other major services were down Friday

Someone attacked a key part of the Internet's infrastructure Friday morning, causing some major services such as Twitter, Spotify and Airbnb to be inaccessible for some users.

The attack targeted Dyn, a company that helps people connect to websites, with a huge amount of traffic in an attempt to knock the service offline, according to Dyn's director of internet analysis, Doug Madory. The digital assault appears to have started around 7:30 a.m. ET, and Dyn said it was resolved at roughly 9:20 a.m.

The service Dyn provides is called the Domain Name System. It works sort of like a phone book for the Internet - it translates URLs into the numerical IP addresses for the servers that actually host sites so your browser can connect to them.

This type of attack is commonly known as a distributed denial of service, or DDoS attack. The effects of the attack were intermittent, and many of the details remain scarce, although it appears to have primarily affected users on the East Coast, according to Dyn.

Madory said that the company may have been the target of a similar type of attack as the one that hit journalist Brian Krebs earlier this year. In that case, someone hijacked unprotected Internet-connected devices like webcams to bombard his site with record levels of traffic.

Dyn provided assistance to Krebs while he was investigating the attack and recently presented research on the case - which may have caused the service to be targeted, according to Madory.

"We were concerned about some blowback from the stuff about Krebs, but we made a decision that it was important work, and we wanted to be part of the solution for everybody's sake," he said.

The potential power of DDoS attacks has increased dramatically in recent years. Even Dyn, which also provides services to help people mitigate DDoS attacks, struggled under the load of the Friday traffic assault.

"Nobody can take on the scale of these attacks these days," said Madory.