Win32.Worm.Downadup worm made its first appearance late November 2008, exploiting the MS08-067 vulnerability to spread unhindered in local area networks. Its purpose was to install rogue security software on infected computers.
In late December, BitDefender Labs uncovered a new version of the worm called Win32.Worm.Downadup.B. The malware comes with a list of new features, aside from the present spreading routine, which has shown signs of improvement.
The worm now uses USB sticks to spread. By copying itself in a random folder created inside the RECYCLER directory, used by the Recycle Bin to store deleted files, and creating an autorun.inf file in the root folder of the drive, the worm automatically executes if the Autorun feature is enabled.
The worm also 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 nearly impossible to gather from an infected computer. Additionally, it removes all access rights of the user, except execute and directory usage, 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 disables Windows updates and certain network traffic, optimizing Vista features to ease its spreading.
Win32.Worm.Downadup.B comes with a domain name generation algorithm similar to the one found in botnets like Rustock. It composes 250 domains every day and 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.