These are temporary directories created by .MSI files. MSI files are used to install applications. Have you installed any old software lately?
Using the root drive for temp files is a method used back before Windows XP SP3 was released.
To delete the files, you'll probably have to take ownership of the directories and their contents.
This command should do so. Careful though, this command should be used with caution as it will pretty much destroy any folders in the root of C: which start with "msi", which on a properly maintained system should not exists.
You will need to open the cmd prompt as admin.
FOR /F "delims=*" %I IN ('DIR /B "C:\msi*"') DO ( TAKEOWN /F "%I" /R && RD /Q /S "%I" )