Microsoft claims that this is a known issue for a few ASUS PC models
Even though it was designed to be easy as pie, the Windows 8.1 update process is not at all that simple, with many users experiencing all kinds of issues when trying to deploy it.For example, some users are now claiming that after installation Windows 8.1 places a small watermark on the desktop saying that “Secure Boot isn’t configured correctly. Build 9600.”
Microsoft indicates that this is a known issue with a few ASUS PC models and recommends users to either turn on Secure Boot or try to configure it correctly from the BIOS menu of the computer.
“Secure Boot helps increase the security of Windows 8.1 and Windows RT 8.1 PCs by stopping unauthorized software from running. If you see a ‘Secure Boot isn't configured correctly’ message in the lower-right corner of the desktop, it means that Secure Boot has either been turned off or hasn't been set up correctly on the PC,” a Microsoft support engineer said.
“To turn on or set up Secure Boot, we will need to use the BIOS menu for the PC. Different PCs have different BIOS menus, so you may need to contact the PC's manufacturer for instructions. If you have turned off Secure Boot and added own drivers then you might need to reset the PC to its original state before you can turn on Secure Boot.”
While this could be quite a difficult task for many beginners who hoped to get a seamless updating process, it’s not yet clear if Microsoft plans to address the issue and roll out a patch to correct the problem.
At this point, the Windows 8.1 update is still displayed in the Store for all ASUS PCs, so some of you might still experience the aforementioned issues once installation comes to an end.
Update (October 21, 2013): Microsoft has provided more details on the Secure Boot error and provided a few tips for users trying to fix it.
Update 2 (October 22, 2013): Redmond has now released more details on this error, along with more instructions on how to fix the Secure Boot error.
Update 3 (October 23, 2013): how to fix the Secure Boot error on Dell machines.
Update 4 (October 23, 2013): here is a workaround for the Secure Boot issue in case you're using Intel hardware.
Update 5 (October 30, 2013): Microsoft has finally rolled out a patch for the Secure Boot error.