What is the default boot option for Windows 8 ? Which boot option should be use Secure or Measured ?
Windows 8 supports a feature of the UEFI specification known as "Secure boot", which uses a public-key infrastructure to verify the integrity of the operating system and prevent unauthorized programs such as bootkits from infecting the device.
The official description of Measured Boot is as follows:
As antimalware (AM) software has become better and better at detecting runtime malware, attackers are also becoming better at creating rootkits that can hide from detection. Detecting malware that starts early in the boot cycle is a challenge that most AM vendors address diligently. Typically, they create system hacks that are not supported by the host operating system and can actually result in placing the computer in an unstable state. Up to this point, Windows has not provided a good way for AM to detect and resolve these early boot threats. Windows 8 introduces a new feature called Measured Boot, which measures each component, from firmware up through the boot start drivers, stores those measurements in the Trusted Platform Module (TPM) on the machine, and then makes available a log that can be tested remotely to verify the boot state of the client.
So Measured Boot is meant for anti-malware vendors and not end users. If your system supports it (has UEFI) you can use Secure Boot.
Your System must have the UEFI capability if you want to use Secure boot option otherwise it is not possible to use Secure Boot.If your system have UEFI and but you want to run any linux distro's then it is not possible to use linux without disabling secure boot until now.In future it may change. For Your Reference: