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What are Thumbs.db files for? I've seen them mostly in picture folders. Wherever pictures like icons and wallpapers are located, a Thumbs.db is automatically generated. I've deleted them many times, but they just appear again after some time.

I initially thought that these files were related to a virus, but they are not because my antivirus gave them a clean chit. I also tried Combofix.

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thumbs.db is where the thumbnail images for files are stored. They will only be visible if you have your folder options set to display hidden and system files. They are not viral.

If you delete a thumbs.db file, the next time you open that folder, Windows will have to re-determine the thumbnail for each file.

Also, in Folder Options, selecting "Do not cache thumbnails" will prevent the thumbs.db files from being created.

However, these files help the computer navigate through your directories more quickly, so unless you have a specific reason for not needing or wanting them, just leave them alone.

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This means that if you delete images, the thumbnails may still be recovered. There is forensic software available to recover images from Thumbs.db files. – TRiG Sep 1 '11 at 17:14
Historically, there was an exploit where Microsoft allowed executable code in thumbs.db which lead to some very nasty viruses. – Malfist Sep 1 '11 at 18:03
So if I don't use the thumbnail view till then they will not appear? – avirk Sep 2 '11 at 11:17
@avirk: Yes and no. It's always more complex than that. I believe the application icon images may be cached there too, but I am not completely sure. You will probably see fewer of them if you turn off thumbnail previews, but they won't go away completely. But you can rest assured, a thumbs.db file is one of the least likely files to end up being viral. If they are annoying, you should probably not set your computer to show hidden files. – music2myear Sep 2 '11 at 14:21
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From https://secure.wikimedia.org/wikipedia/en/wiki/Windows_thumbnail_cache

On Microsoft Windows operating systems (starting with Windows 2000), a thumbnail cache is used to store thumbnail images for Windows Explorer's thumbnail view. This speeds up the display of images as the smaller images do not need to be recalculated every time the user views the folder.

...

Thumbs.db files are stored in each directory that contains thumbnails on Windows systems.

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