The number of Internet of Things (IoT) devices infected with Mirai has increased considerably in the past few weeks after the malware’s author decided to make its source code public.
The first reports about Mirai were largely ignored by the industry, but the massive distributed denial-of-service (DDoS) attacks launched against the website of journalist Brian Krebs and hosting provider OVH brought the Trojan into the spotlight.
When he decided to release the source code, the author of Mirai claimed his creation had infected as many as 380,000 devices, but the number had started to drop after the malware made the news.
Researchers at Level3 Communications have been monitoring Mirai and determined that the number of bots more than doubled following the source code leak. By monitoring the malware’s command and control (C&C) servers, the company has identified nearly 500,000 infected IoT devices, and the actual number is likely even higher. These devices are part of multiple new botnets created after the source code was made public.
In some of the DDoS attacks observed by Level3, cybercriminals used as many as 100,000 bots against a single target.
Experts from various security firms warned that there are hundreds of thousands of devices from vendors such as Taiwan-based AVTECH, and China-based Dahua Technology and XiongMai Technologies that could easily get infected with Mirai malware.
While more than 80 percent of bots are DVRs, the malware is capable of finding and infecting various types of products, including routers, IP cameras, Linux servers and even rugged gateways from Sierra Wireless.
According to Level3, more than a quarter of infected devices are located in the United States, followed by Brazil (23%) and Colombia (8%). Experts pointed out that nearly a quarter of Mirai bots had also been infected with Gafgyt (aka BASHLITE), another highly popular IoT malware.
“Such a high overlap indicates that multiple malware families are targeting the same pool of vulnerable IoT devices,” Level3 explained in a blog post.
Interestingly, researchers noticed that Mirai’s C&C servers had been targeted on several occasions in DDoS attacks launched using BASHLITE botnets.
“With the recent and frequent introduction of new Mirai variants, we expect continued DDoS activity from Mirai botnets,” experts said. “The structure of these botnets is evolving as different owners adapt the malware. In some cases, we see the new variants running all of their infrastructure on one or two hosts, as opposed to the original Mirai variant which had many different hosts and frequently changed IPs to avoid detection or attack.”