A new variant of MyDoom worm - Mydoom.S, was found on August 16th, 2004. The worm spreads like its previous variants.
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The worm's file is a PE executable 27136 bytes long packed with UPX file compressor. The unpacked worm's size is about 53 KiB.
The worm will attempt to download an executable from four different URLs stored within its body, such URLs point to two different sites (www.richcolour.com and zenandjuice.com). These sites were shut down by 18th of August, 2004.
Mydoom copies itself as "winpsd.exe" file to Windows System directory and creates a startup key for the copied file in Windows Registry:
where %WinSysDir% represents Windows System folder. As a result, the worm's file is started every time Windows starts.
The worm creates a mutex named '43jfds93872'.
The email-spreading function will expire on August 20th, 2004. After this the worm should not send emails any more.
The worm spreads in emails. Before spreading it collects email addresses from an infected computer. The worm reads Windows Address Book file, reads files in Temporary Internet Files folders and Windows System folder. Files with the following extensions are checked:
The worm doesn't send itself to email addresses that contain any of the following substrings:
The worm spreads in emails as follows:
The worm fakes the sender's email address. It uses the following user names for the fake email address:
The worm alters the infected computer's hosts file in order to prevent the local user and applications from reaching the Anti-Virus vendors' websites, including f-secure.com and www.f-secure.com.