Index.dat

In the Microsoft Windows operating system, index.dat is a file used by the Internet Explorer web browser. The index.dat file functions as an active database, which runs as long as a user is logged on in Windows. It functions as a repository of redundant information, such as web URLs, search queries and recently opened files. Its role is similar to that of an index file in the field of databases, where a technique called "indexing" stores the contents of a database in a different order to help speed up query responses. Similarly, when the Autocomplete function is enabled in Internet Explorer, every web address visited is sorted in the index.dat file, allowing the Internet Explorer to attempt to find an appropriate match when a user types in an edit field. Separate index.dat files exist for the Internet Explorer history, cache, and cookies.

Note: .dat is a commonly used filename extension for a number of different types of data files (a file that is not human-readable or that does not hold a document-based binary file). Thus one might well encounter a file named index.dat that is not a part of the Windows operating system or of Internet Explorer.

Controversy

Internet privacy groups contend^{[citation needed]} that the use of index.dat files in the Windows operating system is an invasion of privacy. One of their main complaints is that the index.dat files cannot be deleted or erased easily, because they are always open when Windows is running. Open or "locked" files cannot be deleted in any way when the process using them is running. Also, when this file grows larger, degraded web performance will occur.^{[citation needed]}

Another contention is that the operating system gives a false sense of security. Even after the user has cleared the internet cache folder, there is no way to completely disable it, which means that the various index.dat files on Windows continue to store all the visited web addresses and cookies and some temporary files. Also, removing single entries from index.dat files, for example through Windows Explorer, will only remove them from the visual display by Windows Explorer, not from the file itself until the next cleanup. While this can be seen a negative, marking single entries as deleted instead of erasing them is typical database behaviour and usually implemented to speed up removal operations, not to keep a backdoor to removed data.

While some may claim that the Windows Operating System even hides these files, Windows Explorer offers a detailed view of the content of index.dat files when browsing the folders that contain these files, even allowing to remove sepecific entries, so others actually see this as a feature.

Various free programs, among them CCleaner and Unlocker, can remove completely remove index.dat files until they get recreated by Windows.

External links

• Windows Networking Team blog about Index.dat (followup Q&A)
• How to remove index.dat (Site has broken links)
• A Cleanup API for Windows - details on how to delete index.dat files