Not all vulnerabilities utilize cryptic knowledge to hack into the underlying core of an operating system. Master Boot Record viruses have been infecting MBRs since the DOS days, but have since given way in popularity to network and scripting type hacks. It was discovered in 2005 that NT based Windows systems were susceptible to rootkits via a usermode level attack on the MBR. At the end of 2007, security researchers discovered the bootsector programming tutorials have existed for years and there is an abundance of open source examples for Linux loaders like GRUB.