Private browsing is a relative new mode that has been added to several popular web browsers recently.
It allows a user to interact with the web browser like in normal mode but will prevent some data records on the local system.
Data that is accumulated during the private browsing sessions is only temporarily available which is the core difference to the normal browsing mode.
This means that the web browser's history or the temporary Internet files will not contain clues about the websites that the user visited while in private browsing mode.
This does not take care of remote traces and some local traces such as the DNS cache remain untouched as well.
Another exception to that rule is Flash content, so called flash cookies or local shared objects, are still stored on the system and an analyst could use those to uncover the websites that placed them on the computer even while using private browsing modes.
This is going to change with the release of Flash 10.1 which will automatically recognize when a browser is in private browsing mode and abide to its rules. This essentially means that Flash Player 10.1 will automatically clear any data that has been created during the private browsing session so that this data cannot give clues about the websites the user visited during that time.
Private Browsing mode is currently supported in Internet Explorer 8, Mozilla Firefox 3.5 and Google Chrome 1 or higher. Safari 2 is also offering private browsing mode which is currently not supported by Flash 10.1 (but will be in the future).
Flash content that has been stored on the computer system before starting the private browsing mode will remain on the computer. They will however be inaccessible during private browsing mode.
Starting with Flash Player 10.1, Flash Player actively supports the browser's private browsing mode, managing data in local storage so that it is consistent with private browsing. So when a private browsing session ends, Flash Player will automatically clear any corresponding data in local storage.
Additionally, Flash Player separates the local storage used in normal browsing from the local storage used during private browsing. So when you enter private browsing mode, sites that you previously visited will not be able to see information they saved on your computer during normal browsing. For example, if you saved your login and password in a web application powered by Flash during normal browsing, the site won't remember that information when you visit the site under private browsing, keeping your identity private.
Flash Player will not store any changes made to the Global Settings Manager which does have the consequence if a web site or application requests additional storage space. The request will simply be denied which is why Adobe developers have increased the default local storage limit in private browsing to 1 MB (opposed to the 100 KB default in normal mode).
Flash Player does not save any information—including settings—in private browsing mode, since this information might reveal sites that you visited while using private browsing. Accordingly, settings options will be hidden. Tabs that modify domain-specific settings such as privacy (camera and microphone access) and local storage will not be displayed. Since you cannot set domain-specific settings in private browsing mode, Flash Player will use default settings from the global Settings Manager.
Additional information about Flash Player 10.1's new private browsing support are accessible at the Adobe Devnet.
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