After running CCleaner with the Explorer thumbnail cache option selected, I noticed that there were still some (rather large) files, in:
C:\Users\ <user> \AppData\Local\Microsoft\Windows\Explorer
These files include:
thumbcache_32.db
thumbcache_96.db
thumbcache_256.db
thumbcache_1024.db
thumbcache_idx.db
thumbcache_sr.db
I have tried running CCleaner as Admin, as the "User", and as user "run as administrator" -- but the Explorer thumbnail cache files remain. I am tempted to delete these myself, but there are also a couple of other system files in that folder with "etl" extensions that I don't know the purpose of, and would rather not mess with it unless I fully understood the consequences.
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CCleaner v3.01.1327
MS Windows 7 Home Premium 32-bit