I recently placed about 3 GB worth of my university files on a USB drive. After a few days, I tried to access the files on the USB. So, I opened the 'My computer' folder, which is when I noticed that the removable drive showed '164 MB of 3.93 GB free' but there was a red bar (instead of blue) that signified the amount of space covered. I found that a little puzzling.
Anyway, I opened the USB drive to find that all my folders had become files. There was no symbol (i.e. it was empty) beside the names to indicate the program which would open the file. And each of them had 4.00 kB of space. I was in panic. And I was also surprised because although the USB had more than 3.00 GB covered, each of the folders(/files) was only 4.00 kB.
So, I clicked on Properties. Then I went to Tools to check the drive for errors. After the analysis, I found a hidden folder called FOUND.000. I found more than 5000 CHK files in it. I copied them to my Desktop, ran the Disk Defragmenter program on Windows and used Unchk to recover the data. The program recovered only the first 1192 files and a lot of them were in Winrar format (even though the original files were not). I could not recover the rest of the files.
I checked the USB drive for errors several time afterwards. After the first such analysis, FOUND.000 became ...