The files are related to SSL certificates issued through the Windows webserver, IIS.
A solution to delete these files is suggested here:
OK so I have found a way to clear down the folder: forfiles /d -90 /C
"cmd /c del * /F /A:AS"
This looks for files older than 90 days and runs cmd - the del command
with force option and files with attributes A and S (archive &
system). I dont know why it wasn't working without the /A:AS on the
end, maybe becasue they are system files.
Forfiles is a utility to perform batch operations on multiple files.
CAUTION: before you proceed to remove the files, make sure they are not crucial to any production-critical web sites !