File that contains metadata describing the security zones associated with another file; generated automatically when a file is downloaded from the Internet or received as an email attachment; often created by Internet Explorer.

Zone identifier files are also known as "alternate data stream" (ADS) files, since they are only used to describe other files. They have the same filename as the original file, followed by a colon and the text "Zone.Identifier." For example, the file "download.exe:Zone.Identifier" may be saved along with a downloaded file named "download.exe." Windows uses zone identifier files to manage security settings for downloaded files. Since the files are referenced by the operating system, they are not meant to be opened manually. When the original file is deleted, the corresponding zone identifier file is automatically removed by the operating system. Zone identifier files are hidden by default, but may be visible if the "Show Hidden Files" option is turned on.