By Marcos Colon

The malware that preys on Internet of Things (IoT) devices to build botnets that can launch large distributed denial-of-service (DDoS) attacks is spreading like wildfire.

After the malware’s creator release its source code, IoT devices infected by Mirai have increased from 213,000 to 493,000 since the source code was released near the start of October, according to global network company Level 3 Communications.

“The true number of actual bots may be higher based on an incomplete view of the infrastructure,” the company wrote in a blog post.

Cyber attackers have been working on new variants of the malware since the source code’s release, which leads Level 3 to expect “continued DDoS activity from Mirai botnets.” Earlier this month, researchers noticed the botnets leverage a list of more than 60 combinations of usernames and weak default passwords to scan the internet for insecure IoT devices.