A new variant of MyDoom worm - Mydoom.U, was found on September 9th, 2004. This worm variant is similar to previous ones. It spreads in emails with different subject and body texts, downloads and activates a backdoor.
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The worm is a PE ( Portable Executable) file 18200 bytes long packed with UPX file compressor. The unpacked file's size is over 44 kilobytes.
When run, the worm creates a mutex 'qwedefacedRDE', copies itself as WINSPF32.EXE to Windows System Directory and creates a startup key for that file in System Registry:
where %WinSysDir% represents Windows System directory.
Additionally, the worm copies itself to the 'Start Menu\Programs\Startup\' folder of a current user as RX32HH00.EXE file.
The worm spreads by sending its infected attachment to all email addresses found on an infected computer. The worm looks for email addresses in Windows Address Book and in the files with the following extensions:
The worm avoids sending emails to email addresses that contain any of the following substrings:
The subject of infected emails is selected from the following variants:
The body of infected emails is selected from the following variants:
The worm can send itself as an executable attachment or in a ZIP archive with one of the following names:
The worm can also attach a fake virus scan report to its message:
where the antivirus mentioned can be any of the following:
The worm fakes the sender's address and uses the following list of first names to compose the fake address:
It uses the following list of last names to compose the fake address:
It uses the following list of domain names to compose the fake address:
The worm downloads a backdoor from one of the websites and activates it. The backdoor is known as 'Surila.I' or 'BackDoor-CEB.c' and is downloaded from the following websites:
After September 20th, 2004, 01:18:31 the worm stops working and deletes its file from the hard drive.