A typical example query is: intitle:"index of" "parent directory"
When you append the word updated to the query, you are filtering these open directories to show those that contain files or folders named "updated," or directories where the server has recently modified the file timestamps. intitle index of updated
Searching for intitle:index.of updated is in most jurisdictions—it's just using a search engine. However, what you do with the results defines legality. A typical example query is: intitle:"index of" "parent