User Account Control (UAC) is a security enhancement in Windows introduced in Vista.
It makes applications that run by administrators, by default, only have access to what limited users would have access to. Another way to say this is that applications run at medium integrity level by default.
If an application needs more privileges, it need to request it, and Windows will show a UAC dialog. If you press Yes to elevate on the UAC dialog, the process is said to be running as a high integrity process.
UAC can be disabled, and when it is, applications in Windows Vista and Windows 7 run as high integrity processes by default.
This changes in Windows 8, if UAC is disabled, your applications will no longer run as a high integrity process, they will run as a medium integrity process.
Applications can request elevation to a high integrity process when UAC is off explicitly and no UAC dialog will be shown.
We first realized this in Firefox because we noticed the update service was being used for all updates in Windows 8, even when UAC is off.
We designed the update service to only use the service when UAC is on though.
So this change broke that design choice, and to fix it we need to check if the process is running on Windows 8 and if UAC is off.
If those conditions are met we would elevate our process which would not produce a UAC dialog.
Overall this is a great change by Microsoft though. It makes Windows more secure when users disable UAC. It’s good to know about if you develop software for Windows.