Threat description




Finaldo is a mass-mailer, virus and network worm. It is a very fast infector, it infects EXE, OCX and SCR files. It also infects ASP, HTM and HTML files with a small script code that opens a specific EML file. Due to numerus bugs the worm fails to work correctly and often causes crashes or even makes a system unusable after infection.


Automatic action

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.

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You may also refer to the Knowledge Base on the F-Secure Community site for more information.

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Technical Details

Finaldo worm's dropper that is received by e-mail 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 e-mails from MAPI-compatible e-mail browsers and 'replies' to existing e-mails by sending itself (EML file with encoded worm's body) to sender's e-mail addresses. The worm deletes sent message from outgoing message folder. It should be noted that e-mail 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).

Finaldo also looks for *.ASP, *.HTM and *.HTML files and appends a small javascript code to the end of these files. This code is almost the same as Nimda worm uses to infect such type of files. But this routine doesn't seem to work. The worm should also drop its EML files to remote and local systems (like Nimda does), but this functionality fails too.

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

By the time of this description creation Finaldo was not in the wild. F-Secure Anti-Virus detects Finaldo virus-worm with the latest updates.

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