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Local shared object

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Local shared object

A local shared object (LSO), commonly called a Flash cookie (due to its similarity with an HTTP cookie), is a piece of data that websites that use Adobe Flash may store on a user's computer. Local shared objects have been used by all versions of Flash Player (developed by Macromedia, which was later acquired by Adobe Systems) since version 6.

Flash cookies, which can be stored or retrieved whenever a user accesses a page containing a Flash application, are a form of local storage. Similar to cookies, they can be used to store user preferences, save data from Flash games, or track users' Internet activity. LSOs have been criticised as a breach of browser security, but there are now browser settings and addons to limit the duration of their storage.

Local shared objects contain data stored by individual websites. Data is stored in the Action Message Format. With the default settings, the Flash Player does not seek the user's permission to store local shared objects on the hard disk. By default, an SWF application running in Flash Player from version 9 to 11 (as of Sept 1, 2011) may store up to 100 kB of data to the user's hard drive. If the application attempts to store more, a dialog asks the user whether to allow or deny the request.

Adobe Flash Player does not allow third-party local shared objects to be shared across domains. For example, a local shared object from "www.example.com" cannot be read by the domain "www.example.net". However, the first-party website can always pass data to a third-party via some settings found in the dedicated XML file and passing the data in the request to the third party. Also, third-party LSOs are allowed to store data by default. By default, LSO data is shared across browsers on the same machine. As an example:

This is distinct from cookies which have directory isolated storage paths for saved cookies while LSOs use a common directory path for all browsers on a single machine.

Flash games may use LSO files to store the user's personal game data, such as user preferences and actual game progress. Backing up files such as these requires some technical understanding of software. However, both browser updates and programs designed to remove unused files may delete this data.

To prevent cheating, games may be designed to render LSO files unusable if acquired from another location.

As with HTTP cookies, local shared objects can be used by websites to collect information on how people navigate them, although users have taken steps to restrict data collection. Online banks, merchants, or advertisers may use local shared objects for tracking purposes.

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