The Feliz trojan appeared on the 1st of January 2000. This trojan is written in Delphi. Being run the trojan first outputs a dialog with a picture and a single button:
When the button is clicked the trojan looks for C:\Windows\ directory and if it is found outputs the final messagebox:
At the same time the trojan deletes the following files:
C:\COMMAND.COM C:\WINDOWS\COMMAND\COMMAND.COM C:\WINDOWS\SYSTEM.DAT C:\WINDOWS\USER.DAT C:\WINDOWS\SYSTEM.INI C:\WINDOWS\WIN.INI C:\WINDOWS\SYSTEM.CB C:\WINDOWS\WIN.COM
Then the trojan passes control to the operating system. At this time the operating system becomes unstable and it will no longer start after next computer reboot.
If C:\Windows\ directory is not found by the trojan it will output a number of messageboxes and pass control to operating system without activating its payload.
Depending on the settings of your F-Secure security product, it will either automatically delete, quarantine or rename the suspect file, or ask you for a desired action.
More information on the scanning and removal options available in your F-Secure product can be found in the Help Center.
You may also refer to the Knowledge Base on the F-Secure Community site for more information.