The cyber attack which darkened a large portion of the US internet on Friday has been mitigated, but officials continue to monitor the situation, the Department of Homeland Security said Monday.
The domain name services company Dynamic Network Services Inc, or Dyn, suffered successive attacks, causing outages for hours for millions of users of brand-name internet services such as Twitter, Spotify and Netflix. Services began to stabilize on Friday afternoon.
Dyn said it was struck by so-called distributed denial of service attacks in which adversaries flood servers with so much traffic they stumble or collapse under the burden.
"At this time, we believe the attack has been mitigated," Homeland Secretary Jeh Johnson said in a statement.
Johnson also said Monday his department was aware of the malware which may have been used in the attack.
"This malware is referred to as Mirai and compromises Internet of Things devices, such as surveillance cameras and entertainment systems connected to the Internet," Johnson said.
The department's National Cybersecurity and Communications Integration Center was develop ways to respond to Mirai and similar malware, according to Johnson.
"The Department has also been working to develop a set of strategic principles for securing the Internet of Things, which we plan to release in the coming weeks."
Mirai was used in an attack last month on a website belonging to the journalist Brian Krebs, a cybersecurity expert and writer who said his site suffered a massive attack of 620 gigabits per second.
Krebs reported Friday that researchers at the security firm Flashpoint had determined that the attack on Dyn had involved Mirai.
Explore further: Ongoing cyber attack hits Twitter, Amazon, other top websites (Update)