Finaldo worm's dropper that is received by email is polymorphic. When the dropper runs, it drops and activates the FINALDOOM.DLL file that is the main virus-worm code. This code is only compressed with UPX and is not polymorphic. The file has hidden attributes and is usually located in \Windows\Temp\ or in \Temp\ folder.
After that the worm creates an EXE file which is its dropper and also creates FINALDOOM.EML file that is a pre-formatted multipartite mime message. The worm then mime-encodes the dropped EXE file into the EML file and deletes the EXE file. The FINALDOOM.EML file is then ready to be sent out.
When spreading Finaldo reads emails from MAPI-compatible email browsers and 'replies' to existing emails by sending itself (EML file with encoded worm's body) to sender's email addresses. The worm deletes sent message from outgoing message folder. It should be noted that email spreading routine might not work due to bugs in Finaldo's code.
The worm uses the 'i-frame' trick and the attachment that has the name '.EXE' can be automatically activated by Outlook, IE 5.0 or 5.01 that do not have latest security patches. This vulnerability is fixed and a patch for it is available on Microsoft site:
Shortly after activation Finaldo runs its spreading routine. It enumerates network resources and starts to look for *.OCX, *.EXE and *.SCR files and infect them. It also infects files on all local hard drives. The infection is appending and polymorphic. Infection size is variable. Infected files might crash immediately when run or shortly after being run. The worm doesn't infect NTOSKRNL.EXE file and files with _winzip_ sections (WinZip self-extracting archives).
The worm also uses stealth techniques to hide its files from being shown in Windows Explorer even if 'Show All Files' option is enabled.
The virus-worm has the following text strings inside:
Finaldoom is coming! Don't worry... It's no harm to your system !
It's only a demo version
Made in china