Windows 7 How to set a write protection on specific file/folder saved at external USB drive?

Folders becoming read-only has been a problem for many users who desperately want to get rid of it and you're out trying to do it. This link discusses the problem: Link Removed
One of the suggested solutions is to use the DOS attrib command to turn read-only off (in your case, on). It isn't clear to me why they would do that from a command line rather than just using Properties in Windows Explorer. However, setting a folder to read-only just makes the files within it read-only, not the folder, itself.

It isn't clear from your post where files are being added and where you want to use the folder. Are you using the phone just to transport the files (write and read from the computer) and the additional files are showing up in the phone? Are they files sent to your phone that you store there temporarily and just download to your computer? Are they files you access on your phone? Are these "spam" files being sent to your phone and automatically stored in a default folder? Is it a folder that you want the ability to add to on-the-fly but you don't want other files being stored there without your permission? Depending on your situation, a couple of things come to mind:

• Can you change the name of the folder? If it is a folder you created, not a "system" folder, this could either confound writing to it or at least make it easy to periodically delete a folder of the old name that contains nothing you want.
• If you are just using the phone to transport files, put them in a ZIP file (read-only if necessary).
• If the unwanted files are incoming spam on the phone, look for a setting on the phone that locks that. Enable it when you are expecting files.

Can you be more specific about the exact nature of the situation?