EMET is Microsoft's Enhanced Mitigation Experience Toolkit.
It is part of the system's protection against attack. EMET can be configured to look for specific perceived threats. Assuming that you are using a work computer, then this will already have been done by your IT people.
It is difficult to tell exactly what the UAC message that you are getting is for. It may simply be that EMET is updating or installing, but it may be that it is trying to stop a detected attack.
There is a description of its use here and a full user guide can be downloaded from Microsoft.