The latest strain of Mirai, the malware that’s been infecting internet routers from Germany’s Deutsche Telekom, has spread to devices in at least 10 other countries, according to security firm Flashpoint.

The company has detected the new Mirai strain infecting internet routers and modems across the globe, including in the U.K., Brazil, Iran and Thailand.

It’s still unclear how many devices have been infected, but Flashpoint estimates that as many as five million devices are vulnerable. “If even a fraction of these vulnerable devices were compromised, they would add considerable power to an existing botnet,” Flashpoint said in a Tuesday blog post.

The malware grabbed headlines on Monday when Deutsche Telekom reported that close to a million customers experienced internet connection problems from the new Mirai strain infecting their routers. Although Deutsche Telekom has offered a software update to stop the malware, security experts worry that the hackers will continue to upgrade Mirai’s source code to infect additional devices.

The original version of Mirai became notorious for quickly enslaving poorly secured IoT devices, such as DVRs and surveillance cameras. This new strain infects routers from a company called Zyxel, using a known flaw with the product’s SOAP (Simple Object Access Protocol) to take them over.

The goal of Mirai is to form a botnet, or an army of enslaved computers that can be used to launch massive distributed denial-of-service attacks that can shut down websites. In October, Mirai botnets were blamed for doing just that in a disruption that slowed internet access across the U.S.

Flashpoint said it's already found this new strain of Mirai creating a botnet to launch “small-scale” DDoS attacks on an IP address in Africa and a cloud hosting provider. The attacks, which lasted between a few minutes and to more than an hour, occurred on Monday and Tuesday.

Hackers have been exploiting the Mirai malware ever since its source code was released on a forum in late September. The developers of this new strain probably wanted to make their Mirai botnet bigger, Flashpoint said.

However, the spread of the new Mirai strain appears to be slowing down, according to Craig Young, a security researcher at Tripwire. On Monday, he estimated the malware was attempting to infect devices at a rate of one every 90 seconds. But as of Tuesday morning, that rate had slowed to about one every six minutes, he said.

Young said the Deutsche Telekom attack was in one sense a failure. The hackers probably never intended to disrupt Deutsche Telekom customers' Internet connections, but simply to secretly infect their routers to grow the botnet, he said.

The way the Mirai strain took over the routers drew too much attention, provoking the German carrier to quickly issue a security patch. “The malware may have been too demanding on the routers, and overloaded them, so they wouldn’t be able to operate,” Young said.

He expects the hackers to keep upgrading Mirai. “Someone will fix the bugs in the code,” he said. “People will also incorporate more exploits related to routers.”