Linux distributions are making slow progress on implementing measures to ensure that their images available for download are bootable on hardware that has secure boot turned on.
Secure boot is a feature of the UEFI, the Unified Extensible Firmware Interface, a replacement for the BIOS.
Microsoft has implemented this feature on hardware certified for Windows 8 in a way that requires the exchange of cryptographic keys; since the company controls the key-signing authority, anyone who wants to create a bootable medium has to necessarily obtain a key from Redmond.
Misinformation is rife about secure boot, simply because people confuse UEFI with secure boot and think that support for the former means support for the latter. Many so-called technical types are as guilty as others of spreading wrong information.