A massive and sustained Internet attack that has caused outages and network congestion today for a large number of Web sites was launched with the help of hacked “Internet of Things” (IoT) devices, such as CCTV video cameras and digital video recorders, new data suggests.

Earlier today cyber criminals began training their attack cannons on Dyn, an Internet infrastructure company that provides critical technology services to some of the Internet’s top destinations.

The attack began creating problems for Internet users reaching an array of sites, including Twitter, Amazon, Tumblr, Reddit, Spotify and Netflix.

At first, it was unclear who or what was behind the attack on Dyn. But over the past few hours, at least one computer security firm has come out saying the attack involved Mirai, the same malware strain that was used in the record 620 Gpbs attack on my site last month.

At the end September 2016, the hacker responsible for creating the Mirai malware released the source code for it, effectively letting anyone build their own attack army using Mirai.

Mirai scours the Web for IoT devices protected by little more than factory-default usernames and passwords, and then enlists the devices in attacks that hurl junk traffic at an online target until it can no longer accommodate legitimate visitors or users.

According to researchers at security firm Flashpoint, today’s attack was launched at least in part by a Mirai-based botnet. Allison Nixon, director of research at Flashpoint, said the botnet used in today’s ongoing attack is built on the backs of hacked IoT devices — mainly compromised digital video recorders (DVRs) and IP cameras made by a Chinese hi-tech company called XiongMai Technologies. The components that XiongMai makes are sold downstream to vendors who then use it in their own products.

The default usernames and passwords on a Web-based administration panel that ships with the products, those machines can still be reached via more obscure, less user-friendly communications services called “Telnet” and “SSH.”

Telnet and SSH are command-line, text-based interfaces that are typically accessed via a command prompt (e.g., in Microsoft Windows, a user could click Start, and in the search box type “cmd.exe” to launch a command prompt, and then type “telnet” to reach a username and password prompt at the target host).

“The issue with these particular devices is that a user cannot feasibly change this password,” Flashpoint’s Zach Wikholm told KrebsOnSecurity. “The password is hardcoded into the firmware, and the tools necessary to disable it are not present. Even worse, the web interface is not aware that these credentials even exist.”

Flashpoint’s researchers said they scanned the Internet on Oct. 6 for systems that showed signs of running the vulnerable hardware, and found more than 515,000 of them were vulnerable to the flaws they discovered.

“I truly think this IoT infrastructure is very dangerous on the whole and does deserve attention from anyone who can take action,” Flashpoint’s Nixon said.

BALAJI is a Security Researcher (Threat Research Labs) at Comodo Cybersecurity. He is a Certified Ethical Hacker, Editor-in-Chief, Author & Co-Creator of GBHackers On Security