W32/Ridnu.D is a virus that spreads to other computers by copying its code to other files or programs.
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 modifies system permissions in order to hide itself.
It uses several methods in order to avoid detection by antivirus companies:
- 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.
- It terminates its own execution if it detects that a debugging program is active.
W32/Ridnu.D 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.
- File infection: it infects different types of files, which are then distributed through any of the usual means: floppy disks, email messages with attachments, Internet download, files transferred via FTP, IRC channels, P2P file sharing networks, etc.
W32/Ridnu.D uses the following infection strategies:
- Resident: once it has been run, the virus goes memory resident and stops functions belonging to the operating system. Therefore, every time the operating system or an application tries to access any of these functions, the virus will activate and infect new files.
- Overwriting: it deletes the content of infected files and substitutes it with its code. Therefore, these files will be unusable and cannot be restored. When users try to open the original file, they will actually be running a copy of the virus.
- Companion: it renames files on the infected computer. This virus also makes copies of itself, and assigns them the original names of the files it has renamed. When users try to open the original file, they will actually be running a copy of the virus.
- Prepending: it enters its code at the beginning of the file it infects. By doing this, it ensures that the virus is run every time the infected file is executed, but without interfering the functioning of the file.