1. A method implemented at least in part by a computer, the method comprising: obtaining an indication that a file has changed; checking whether the file is in a protected namespace, files in the protected namespace designated for back up to backup storage; if the file is in the protected namespace, adding any new tokens included in the file to an index, adding, to the index, references from the new tokens to the file, and keeping previous references to the file in the index; and if the file is not in a protected namespace, deleting references to the file, if any, that existed previously in the index and re-indexing the file to add references to the file in the index.