First of all, the worm can now use USB sticks to spread. By copying itself in a random folder created inside the RECYCLER directory used by Recycle Bin to store deleted files and creating an autorun.inf file in the root folder of the drive, the worm will automatically get executed when the device is plugged in the computer if the Autorun feature is enabled.
Second of all, the worm patched certain TCP functions to block access to security related websites by filtering every address that contains certain strings. This makes it harder to remove since information about it is hard, nearly impossible, to gather from an infected computer. Additionally it removes all access rights of the user except execute and directory traversal to protect its files.
The worm is also built to avoid antivirus detection by working with rarely used APis in order to avoid virtualization technologies. It is also disabling windows update and certain network traffic optimizing vista features to ease its spreading.
To complete the feature list, Win32.Worm.Downadup.B comes with a domain name generation algorithm similar to the one found in botnets like Rustock. It uses date and time to compose 250 domains every day, which it checks for updates or other files to download and install.
Having a state of the art update system, a good protection scheme and many people that don’t patch their systems, this worm has great potential to become a rival to already established botnets like Storm or Srizbi.
For more technical details please visit the BitDefender description: Win32.Worm.Downadup.Gen