What is SUPPORT_388945a0

What is SUPPORT_388945a0 USER ?

Answer : 
The Full Name of This User in Windows is :  CN=Microsoft Corporation, L=Redmon,S=Washington,C=US ;

User Description as Per Microsoft is : This is a Vendor's(i.e. Microsoft's) Account for The Help and Suppor Service.

It Means : This Account is used by Microsoft Support Team Whenever you Communicate with Them The Use This Account to Log-in to Your Computer.