VBootkit is a Windows Vista Bootkit designed to compromise security while the system is in the booting process. The idea is to do this without being detected by hooking INT 13, used for HDD reading. Funnily enough Brain, the very first computer virus, did the same. It infected boot sectors and when a program wanted to read the boot sector, Brain would show the original sector. Of course, the particularly bad thing about this attack is that Vistas kernel protection will make it impossible to detect it.”]
Source: https://securelist.com/the-more-things-change/30313/