Prevent Upload file/or attachment having same name as existing file

I notice a Filemanager and attachment modules.

Haven't installed either.

I need to prevent upload file from having the same file name as existing file name.

It would be good if popup or warning were given when trying to upload a file with the same name as an existing file.

Naturally, I wouldn't want to allow duplicate files names so it would have to be required.

I would need same funtion for upload of images.

Thanks