I noticed that every single folder inside my pictures folder has a new hidden folder named ".Thumbnails". It has thumbnails of its parent folder. Thumbnails are actually quite large ranging from 160 pixels to 512 pixels in one dimension.
I noticed this with unusual activity in my backup process. All folders seems to be created on July 18 between 9:30 pm to 11 pm. I recently two apps iTunes on July 24 and Crashplan (another backup software) on July 19.
I do not think these are windows default folders. I want to find out which application is creating these folders and why it started suddenly. And lastly, how can I get rid of all of them easily?
Update: I find out that I used SyncToy 2.1 around the same time to copy my user account to a network drive.