The malicious downloader Nemucod, normally associated with ransomware, has reportedly switched payloads in its most recent known campaign, opting instead to infect victims with Kovter, a backdoor trojan capable of click fraud.
According to an ESET blog post, bad actors are taking advantage of Nemucod's ability to control its own click-function via an embedded browser, activating as many as 30 threads at once in order to visit sites and click on ads. To avoid unwanted attention, Kovter can ramp up or scale back its ad-clicking activity based on an infected machine's available memory and CPU usage. It also scans for virtual environments to evade analysis.
Initial infection of Nemucod typically occurs when a victim is fooled into opening a malicious, emailed zip attachment posing as an invoice. In the past, a Nemucod attack typically led to a secondary infection of Locky or TeslaCrypt ransomware, the report explained.
