Why?
A bug within Windows Defender 18100.5 may cause hundreds, thousands, or millions of files to be generated. This bug is resolved with version 18100.6.
Action Needed
If your machine is running low on storage space, validate if Windows Defender has created a large number of files.
Details
Check Windows Defender Folder
Open File Explorer and search for:
C:\ProgramData\Microsoft\Windows Defender\Scans\History\Store\
You can sort by Date Modified to determine when files were created. If this folder is filled with recent files, it is recommended you delete them.