There are many good reasons to use the new UEFI Secure Boot under Windows 10 but there are also numerous reasons not to.  The latest is an issue with a specific Windows Update patch which was recently changed from an optional update to a recommended update.  For systems using an ASUS motherboard and running Windows 7 this can be a bit of a bother as your Secure Boot will report that the OS has unauthorized changes and will refuse to boot.  If you can get at your UEFI BIOS you can change the OS Type from Windows UEFI mode to Other OS in the boot menu.  If this does not resolve your issue The Register has been told you should contact ASUS for support, as opposed to Microsoft since the issues root cause lies in a feature similar to Secure boot which ASUS added to their boards.

"Windows 7 machines that have installed Microsoft's KB3133977 update may trigger a "secure boot violation" during startup, preventing the PC from loading the operating system, Asus said."

Here is some more Tech News from around the web:

Tech Talk