Nurech.B is a worm that spreads by copying itself, without infecting other files.
It captures certain information entered or saved by the user, with the corresponding threat to privacy:
It affects productivity, preventing tasks from being carried out:
- In the affected computer:
causes system slowdowns.
- In the local network:
it generates a large amount of network activity and consumes bandwidth.
- On remote sites: it mass mails junk mail (spam).
It reduces the security level of the computer:
it terminates processes belonging to security tools, such as antivirus programs and firewalls, leaving the computer defenseless against attacks from other malware; it changes system permissions, decreasing the security level.
It uses stealth techniques to avoid being detected by the user:
- It uses techniques included in its code to hide itself while it is active.
- It injects itself in running processes.
- It deletes the original file from which it was run once it is installed on the computer.
- It modifies system permissions in order to hide itself.
It uses several methods in order to avoid detection by antivirus companies:
- It terminates its own execution if it detects that it is being executed in a virtual machine environment, such as VMWare or VirtualPC.
- It prevents scanning tools from running, such as Windows Registry Editor, FileMonitor, etc.
- It terminates its own execution if it detects that a memory dump program is running, such as Procdump.
- Its code is encrypted and it is only decrypted when it is going to run. Because of this, its code is not legible through a memory dump.
- It terminates its own execution if it detects that a debugging program is active.
Nurech.B uses the following propagation or distribution methods:
- Exploiting vulnerabilities with the intervention of the user: exploiting vulnerabilities in file formats or applications. To exploit them successfully it needs the intervention of the user: opening files, viewing malicious web pages, reading emails, etc.
- Email: sending emails that include a copy of itself as an attachment. The computer is infected when the attachment is run.
- It is dropped or downloaded to the computer by other malware specimens, for example: Nurech.Z.