What is this file extension

I am recently getting a notice (Win10) to select a program to open files with the following extension: .d253cd8.  I google this extension and nothing comes up.  My Norton is always scanning and asking me to restart telling me it has removed threats.  In my old Explorer, the history would show all sorts of place I never went too.

I've done deep scans with 360 Premier but I think it is missing something.