I’m sure other utilities (both free and paid) work well too, but I find Bulk Rename Utility ( http://www.bulkrenameutility.co.uk/Main_Intro.php) quick and easy for hiding an entire drive’s thumbnail files (although you can also do things on a per-folder basis, or even a per-file basis, and if you play around and learn, the filters and options are quite extensive).
(This quick method also assumes there are no other image files on that drive that you don’t want hidden… if there are images you don’t want hidden then you’d have to work folder by folder.)
Step 1:
Click the shared drive that has the thumbs you need hidden.
Change the Selection from “*” to “*.jpg”.
Tick the Subfolders Selection box.
It will take a bit for the program to scan the entire drive looking for .jpg files, so be patient.
Step 2:
Actions – Select All
Step 3:
In _ Prefix _ under _ Add: _ type a single period. (You’ll notice that my thumbs already have one period, and my demonstration will actually prepend a second period to the beginning, but you get the drift.)
Click _ Rename _.
That’s it! When it’s done, those thumbs are now hidden files to the WDTV Live and WDTV Live Plus and will not show up in the WDTV browser… all 1436 of them! And it only took 7 clicks and 5 keypresses once the program was running. 
