What happens when you press 'Clear History' button in Internet Explorer®? Are all the files really deleted or not? The answer is: yes, but not all of them. Additionally, the typed URLs in the drop-down list box 'Address' and the list of recently run objects in the Registry are cleared.

The history folder contains a global index file (Index.dat) and one in each of the different weekly sub-folders. For more details refer to History Inspector. The global index contains complete data, i. e., URLs, page titles and dates. The weekly folders contain also index files but without titles. They are used only to organize the weekly display in Internet Explorer®. All weekly folders are listed in a special Registry key:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Internet Settings\5.0\Cache\Extensible Cache
for IE 5 and Windows® 95.

Weekly folders not listed in Extensible Cache key are not shown in the Browser. To see this practically you may download History Inspector and examine these folders on your computer as well as easily change the Extensible Cache key.

When you press 'Clear History' button in Tools menu | Internet Options of Internet Explorer®, the following actions are performed immediately:

1.     All weekly folders listed in Extensible Cache key are deleted.

2.     The index.dat file of the global folder is not deleted, but the information is changed in such a way that information cannot be retrieved further on. It is locked forever and only new information written into this file can be retrieved.

3.     The entries in the following Registry keys are cleared completely:

HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\TypedURLs (see below).

Note: To have these actions completed, the computer must be shut down and restarted again.

Consequences: weekly folders that are not listed will not be deleted. If the Extensible Cache key has been damaged sometimes, deleting history will not work. On the other hand, if the Extensible Cache key lists weekly folders located anywhere on the computer, they will all be deleted, not only in the current History folder. Therefore, care must be taken before this operation is performed. The index.dat file is not decreased to its minimum size. But this is not a severe problem as it is used to store new information. For a typical size of 1 MB of this file it is not a huge loss of hard disk space. However, as long as the file is not deleted, the information still exists even if it is invisible to the average user. Even the History Reader program cannot get back this information, but for the computer expert it is very easy to retrieve this invisible information as long as it is not overwritten or completely deleted.