Security researchers have discovered that the Smominru malware infected 90,000 machines worldwide during the month of August, with an infection rate of up to 4,700 computers per day.
In its post-infection phase, it steals victim credentials, installs a Trojan module and a cryptominer and propagates inside the network, according to researchers from Guardicore, a data centre and cloud security company.
The botnet uses several methods to propagate, but primarily it infects a system in one of two ways -- either by brute-forcing weak credentials for different Windows services, or more commonly by relying on the infamous EternalBlue exploit, cybersecurity firm Kaspersky said in a blog post last week.
Even though Microsoft patched the vulnerability EternalBlue exploits, which made the WannaCry and NotPetya outbreaks possible, many companies are simply ignoring updates, Kaspersky said.
China, Taiwan, Russia, Brazil and the US have seen the most attacks, but that doesn't mean other countries are out of its scope. For example, the largest network Smominru targeted was in Italy, with 65 hosts infected.
The criminals involved are not too particular about their targets, which range from universities to healthcare providers.
However, one detail is very consistent. About 85 per cent of infections occur on Windows 7 and Windows Server 2008 systems. The rest include Windows Server 2012, Windows XP and Windows Server 2003.
After compromising the system, Smominru creates a new user, called admin$, with admin privileges on the system and starts to download a whole bunch of malicious payloads.
The most obvious objective is to silently use infected computers for mining cryptocurrency (namely, Monero) at the victim's expense.
The malware also downloads a set of modules used for spying, data exfiltration, and credential theft.
On top of that, once Smominru gains a foothold, it tries to propagate further within the network to infect as many systems as possible.
To protect their network, computers, and data from Smominru, users need to update operating systems and other software regularly, Kaspersky said.
It is also important for users to use strong passwords. A reliable password manager that helps you create, manage, and automatically retrieve and enter passwords may help protect you against brute-force attacks.