A new malware threat – named Viro botnet malware – has been detected that combines the file-encrypting capabilities of ransomware, with a keylogger to obtain passwords and a botnet capable of sending spam emails from infected devices.
Viro botnet malware is one of a new breed of malware variants that are highly flexible and have a wide range of capabilities to maximize profit from a successful infection. There have been several recently discovered malware variants that have combined the file-encrypting properties of ransomware with cryptocurrency mining code.
The latest threat was identified by security researchers at Trend Micro who note that this new threat is still in development and appears to have been created from scratch. The code is dissimilar to other known ransomware variants and ransomware families.
Some ransomware variants are capable of self-propagation and can spread from one infected device to other devices on the same network. Viro botnet malware achieves this by hijacking Outlook email accounts and using them to send spam email containing either a copy of itself as an attachment or a downloader to all individuals in the infected user’s contact list.
Viro botnet malware has been used in targeted attacks in the United States via spam email campaigns, although bizarrely, the ransom note dropped on the victims’ desktops is written in French. This is not the only new ransomware threat to include a French ransom note. PyLocky, a recently detected new ransomware threat that masquerades as Locky ransomware, also had a French ransom note. This appears to be a coincidence as there are no indications that the two ransomware threats are related or are being distributed by the same threat group.
With Viro botnet, Infection starts with a spam email containing a malicious attachment. If the attachment is opened and the content is allowed to run, the malicious payload will be downloaded. Viro botnet malware will first check registry keys and product keys to determine whether its encryption routine should run. If those checks are passed, an encryption/decryption key pair will be generated via a cryptographic Random Number Generator, which are then sent back to the attacker’s C2 server. Files are then encrypted via RSA and a ransom note is dropped on the desktop.
Viro botnet malware also contains a basic keylogger which will log all keystrokes on an infected machine and send the data back to the attacker’s C2 server. The malware is also capable of downloading further malicious files from the attacker’s C2.
While the attacker’s C2 server was initially active, it has currently been taken down so any further devices that are infected will not have data encrypted. Connection to the C2 server is necessary for the encryption routine to start. Even though the threat has been neutralized this is expected to only be a brief hiatus. The C2 is expected to be resurrected and larger distribution campaigns can have been predicted.
Protecting against email-based threats such as Viro botnet malware requires an advanced spam filtering solution such as SpamTitan to prevent malicious messages from being delivered to end users. Advanced antimalware software should be installed to detect malicious files should they be downloaded, and end users should receive security awareness training to help them identify security threats and respond appropriately.
Multiple backups should also be created – with one copy stored securely offsite – to ensure files can be recovered in the event of file encryption.