According to the report, Incapsula discovered the infections as part of an investigation into a distributed denial of service attack on what it described as a "rarely-used asset" at a "large cloud service." The attack used a network of 900 compromised cameras to create a flood of HTTP GET requests, at a rate of around 20,000 requests per second, to try to disable the cloud-based server. The cameras were running the same operating system: embedded Linux with BusyBox, which is a collection of Unix utilities designed for resource-constrained endpoints.
The malware in question was a variant of a self-replicating program known as Lightaidra, which targets systems running BusyBox and exploits vulnerable Telnet/SSH services using so-called "brute force dictionary attacks" (aka "password guessing"). Given that many Internet connected devices simply use the default administrator credentials when deployed, calling it a "brute force" attack is probably a stretch.