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.
Based on the settings of your F-Secure security product, it will either move the file to the quarantine where it cannot spread or cause harm, or remove it.
A False Positive is when a file is incorrectly detected as harmful, usually because its code or behavior resembles known harmful programs. A False Positive will usually be fixed in a subsequent database update without any action needed on your part. If you wish, you may also:
Check for the latest database updates
First check if your F-Secure security program is using the latest updates, then try scanning the file again.
Submit a sample
After checking, if you still believe the file is incorrectly detected, you can submit a sample of it for re-analysis.
Note: If the file was moved to quarantine, you need to collect the file from quarantine before you can submit it.
Exclude a file from further scanning
If you are certain that the file is safe and want to continue using it, you can exclude it from further scanning by the F-Secure security product.
Note: You need administrative rights to change the settings.
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:
1. Install the backdoor so that it will be launched next time Windows starts.
2. Removes the entries created when installing from the Windows registry.
3. Reboot a computer.
4. Open a shell that allows a computer to be controlled remotely.
5. 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.