Welcome to the Internet of Evil Things. The attack that disrupted much of the Internet on October 21 is still being teased apart by investigators, but evidence thus far points to multiple "botnets" of Internet-connected gadgets being responsible for blocking access to the Domain Name Service (DNS) infrastructure at DNS provider Dyn. Most of these botnets—coordinated armies of compromised devices that sent malicious network traffic to their targets—were controlled by Mirai, a self-spreading malware for Internet of Things (IoT) devices.

But other systems not matching the signature of Mirai were also involved in the coordinated attack on Dyn. "We believe that there might be one or more additional botnets involved in these attacks," Dale Drew, CSO of Level 3 Communications, told Ars. "This could mean that they are 'renting' several different botnets to launch an attack against a specific victim, in which multiple other sites have been impacted."

The motive may have been blackmail, with the attacker seeking a payout by Dyn to stop. [Update: Dyn has said there was no financial motivation behind the attack.] But Drew warned that the huge disruption caused by the attack "could result in large copycat attacks, and [a] higher [number of] victim payouts [so] as to not be impacted in the same way. It could also be a signal that the bad guy is using multiple botnets in order to better avoid detection since they are not orchestrating the attack from a single botnet source."

Mirai has played smaller roles in previous attacks. It factored into last month’s extended distributed denial of service (DDoS) attack on the website of information security reporter Brian Krebs and an even larger DDoS against the French cloud provider OVH. Mirai clearly was the star of the attack on Dyn, apparently controlling multiple groups of bots.

But even in the midst of the Dyn attack, some of the Mirai-infected devices were being used to attack another target—the infrastructure of a gaming company, according to Allison Nixon, the director of security research at security company Flashpoint. That idea matches up with what others who had some insight into the attack have told Ars confidentially—that it was also pointed at Sony’s PlayStation Network, which uses Dyn as a name service provider.

For now, it's not clear that the attacks on Dyn and the PlayStation Network were connected. And with a criminal investigation underway, a Dyn spokesperson declined to confirm or deny that Sony was also a target. "We are continuing to work closely with the law enforcement community to determine the root cause of the events that occurred during the DDoS attacks last Friday," Adam Coughlin, Dyn’s director of corporate communications, told Ars. "Since this is an ongoing investigation, we cannot speculate on these events."

Regardless of the reasons behind it, the attack on Dyn further demonstrates the potential disruptive power of the millions of poorly protected IoT devices. These items can be easily turned into a platform for attacking anything from individual websites to core parts of the Internet's infrastructure. And Mirai has demonstrated that it doesn't take "zero-day" bugs to make it happen; attackers only need poorly implemented security on devices that can't be easily fixed.

From tiny cameras, mighty botnets grow

Mirai is hardly the first IoT botnet to make headlines. In December 2014, LizardSquad's "stresser" service—built on compromised home Wi-Fi routers—announced that it was ready for business with Christmas attacks on the PlayStation Network and Microsoft's Xbox Live service. (The service was eventually hacked itself.) And while Mirai played a supporting role in the 620-gigabit per second attack on Krebs on Security and the terabit-per-second attack on OVH, those attacks also leveraged Bashlight, another (larger at the time) IoT botnet. By the time it was over, more than 30,000 Internet-connected surveillance cameras and DVRs were involved in the OVH attack. It lasted for over a week.

There are a few things that make Mirai stand out from previous IoT botnets. First and foremost, its code has been published openly on the Internet. On September 30, in the wake of the attacks on OVH and Krebs, someone claiming to be the malware's author published the botnet and command and control (C&C) server code on Hacker Forums. Suddenly, anyone could access step-by-step instructions for its configuration and use.

On the plus side, the published source code gives researchers a great deal of insight into how Mirai operates. On the downside, however, it makes it possible for anyone who can compile the code and has access to Internet-connected servers to build their own botnet. This opportunity provides more ambitious botnet builders a proven platform to improve upon.

The simplicity of Mirai's C&C structure makes scaling it up relatively simple. "One of the things we noticed during the Dyn attack was that the C&C domain would change its address," Nixon explained. "That way, the C&C network could segment its botnet." By simply changing a DNS entry, the attacker could use the same domain to create and operate multiple separate botnets simultaneously.

When a Mirai bot is created, it sends a request to the Domain Name Service for the "A" address of a domain configured by its creator. Once it has the Internet address associated with that "A" address, it locks onto that IP address. "When one C&C server fills up, [the botnet operator] can just change the IP address associated with that 'A' name," Nixon explained. New bots will connect to the new address while older bots continue to communicate with the previously labeled server.

While this scheme can cause problems with resiliency of the botnet—if a C&C server gets identified and its traffic is shut down, the bots fail—it's not a big problem for the botnet long-term. The botnet can easily be re-established from another server by simply re-discovering vulnerable devices.