Is File Upload class creates unique file name when encrypt_name set true?

It's in the User's Guide.

encrypt_name

If set to TRUE the file name will be converted to a random encrypted string. 
This can be useful if you would like the file saved with a name that can not be discerned by the person uploading it.

Thanks for the quick reply.
I already read the guide. My question is, whether it will be a unique name. Because, I am storing all user uploads in a single folder, hence it should not be overwritten at any time.
Also, I could not able to find a way to prefix a unique id to the random filename.
If I manually set a unique file name, unable to determine the original file's extension.

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