Backdoor.Winshell is a hacker's tool that allows an attacker to remotely control a computer where it is installed. An attacker just has to telnet to the preconfigured port of the remote computer and a menu is shown.
This backdoor's file is packed with UPX file compressor, the port it listens to is configurable. It allows the following operations to be performed on an infected computer:
Install the backdoor so that it will be launched next time Windows starts.
- Removes the entries created when installing from the Windows registry.
- Reboot a computer.
- Open a shell that allows a computer to be controlled remotely.
- Download any file from a given URL.
When creating a shell, the backdoor executes cmd.exe or command.com command interpreter, depending on Windows version, and pipes its output to the attacker.
All files detected as Backdoor.Winshell should be deleted from an infected system. If some files are locked while Windows is active, they should be deleted from pure DOS (in case of Windows 9x system) or renamed with a different extension (.EXA for example) with further system restart (in case of NT-based system). After restart the renamed file should be deleted.
[Analysis: Ero Carrera; F-Secure Corp.; July 24th, 2002]