MyDoom.K worm variant appeared on May 21st, 2004. It is functionally similar to MyDoom.E variant, but does not spread to Kazaa file sharing network and does not perform a DoS (Denial of Service) attack. The worm drops a backdoor component that listens on port 3127.
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MyDoom.K worm's file is a PE executable 50176 bytes long compressed with a modified UPX file compressor. The backdoor DLL is a 4608 bytes long, also compressed with a modified UPX file compressor.
When the worm's file is run, it creates a separate thread that generates garbage data file and then opens it with Notepad. Then this thread terminates.
After that the worm drops SHIMGAPI.DLL file into Windows System folder. This file is a backdoor (hacker's remote access) component. It is started as a thread of Explorer from the following Registry key:
Finally the worm installs itself to system. It copies itself as RUNDLL6.EXE file to Windows System directory and creates a startup key for this file in the Registry:
where %winsysdir% represents Windows System directory name.
Additionally the worm deletes the following Registry keys:
The worm spreads itself in email messages. To locate email addresses to spread to, the worm reads Address Book file name from the Registry:
Then it browses through the Address Book file and collects email addresses from there. Additionally the worm looks for email addresses in files with the following extensions:
The worm avoids using email addresses that contain the following substrings:
The worm can fake the sender's email address. It composes email addresses from 2 parts: user name and domain name. Here is the list of user names that the worm uses:
Here is the list of domain names that the worm uses:
The subject for the infected message is selected from the following variants:
The body of the infected message can contain one of the following:
The attachment name can be one of the following:
The attachment can have 2 extensions. In such case the first extension can be:
And the second or the only extension can be:
The worm can also send itseld inside a ZIP archive.
The worm drops a backdoor component that starts as a thread of Explorer and listens to port 3127 for commands from remote hackers.
Additionally the worm tries to connect to 'sipper112.netfirms.com' website. At the moment of creation of this description the site was not accessible because it exceeded its its daily bandwidth limit.