TDL4, also known as TDSS in some circles, is a Root Kit that targets the MBR (Master Boot Record) and is nearly impossible to remove. At one point, it was responsible for a botnet with more than 4 million hosts, earning the title of indestructible. Now, researchers at Damballa have discovered a new iteration of TDSS, which uses a new command and control (C&C) communication method that is helping it push a new click-fraud initiative.