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Local shared object

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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.[1]

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.[2] 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.[3]

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".[1] 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.[4][5] By default, LSO data is shared across browsers on the same machine. As an example:

  • A visitor accesses a site using their Firefox browser, then views a page displaying a specific product, then closes the Firefox browser, the information about that product can be stored in the LSO.
  • If that same visitor, using the same machine now opens an Internet Explorer browser and visits any page from the site viewed in Firefox, the site can read the LSO value(s) in the Internet Explorer browser, and display dynamic content or otherwise target the visitor.

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.

Application to games


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.

Privacy concerns


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.[6] Online banks, merchants, or advertisers may use local shared objects for tracking purposes.[7]

On 10 August 2009, Wired magazine reported that more than half of the top websites used local shared objects to track users and store information about them, but only four of them mentioned it in their privacy policy. "Flash cookies are relatively unknown to web users," the article said, "even if a user thinks they have cleared their computer of tracking objects, they most likely have not." The article further says that some websites use Flash cookies as hidden backups so that they can restore HTTP cookies deleted by users.[8]

According to the New York Times, by July 2010 there had been at least five class-action lawsuits in the United States against media companies for using local shared objects.[9]

In certain countries, it is illegal to track users without their knowledge and consent. For example, in the United Kingdom, customers must consent to the use of cookies/local shared objects:[10][11]

Cookies or similar devices must not be used unless the subscriber or user of the relevant terminal equipment:

  • is provided with clear and comprehensive information about the purposes of the storage of, or access to, that information; and
  • is given the opportunity to refuse the storage of, or access to, that information.
    — Information Commissioner's Office

Local shared objects were the first subject to be discussed in the Federal Trade Commission (FTC) roundtable in January 2010.[12] FTC Chairman Jon Leibowitz has been talking with Adobe about what it describes as "the Flash problem." [13]

User control


Users can disable local shared objects using the Global Storage Settings panel of the online Settings Manager at Adobe's website.[14] However, this places a permanent flash cookie on the computer, informing all other websites that the user does not want flash cookies stored on their computer. Users can opt out of LSOs from specified sites from Flash Player's "Settings", accessed by right-clicking the Player, or using the Website Storage Settings panel; the latter also allows users to delete local shared objects.[15]

Users may also delete local shared objects either manually or using third-party software. For instance, CCleaner, a standalone computer program for Microsoft Windows and Mac OS X, allows users to delete local shared objects on demand. There is also a Firefox add-on, Clear Flash Cookies, which will automatically clear out all LSOs each time the browser is restarted.[16]

Since version 10.3 of Flash, the Online Settings Manager (letting users configure privacy and security permissions via Adobe's website) is superseded by the Local Settings Manager on Windows, Mac, and Linux platforms. It can be accessed via the Windows Control Panel or Mac OS System Preferences.[17] Users of other operating systems still use the Adobe Online Settings Manager. Since at least April 2012 (v, updating by downloading a new Flash version resets the security and privacy settings to the defaults of allowing local storage and asking for media access again, which may be against users' wishes.

Browser control


Browser control refers to the web browser's ability to delete local shared objects and to prevent the creation of persistent local shared objects when privacy mode is enabled. As for the former, Internet Explorer 8, released on March 19, 2009,[18] implements an API that allows browser extensions to co-operate with the browser and delete their persistent data stored when user issues a Delete Browsing History command.[19] However, two years passed since its introduction until Adobe, on March 7, 2011, announced that Flash Player v10.3, which was still in development at the time, supports co-operating with Internet Explorer 8 or later to delete local shared objects.[20]

Also on January 5, 2011, Adobe Systems, Google Inc., and Mozilla Foundation finalized a new browser API (dubbed NPAPI ClearSiteData). This will allow browsers implementing the API to clear local shared objects.[21] Four months later, Adobe announced that Flash Player 10.3 enables Mozilla Firefox 4 and "future releases of Apple Safari and Google Chrome" to delete local shared objects,[20] so since version 4, Firefox treats LSOs the same way as HTTP cookies - deletion rules that previously applied only to HTTP cookies now also apply to LSOs.[22][23] This caused loss of data and backward-incompatible flash application behavior[24] for those Firefox and Flash users who used HTTP cookies and Flash local shared objects for different goals. Mainly this affected flash gamers, who rely on Flash LSOs to store saved games.[25][26] The resulting support requests cannot be solved favorably for Mozilla Firefox users without changes to the browser, because of the introduced equivalence between HTTP and flash cookies.[22][23] Currently, the workaround in use is to either configure the browser to never clear history data and cookies or to revert the part of the changes affecting this use case, using third-party patches.[27]

As for the behavior in browser's privacy mode, Adobe Flash Player 10.1, released on June 10, 2010, supports the privacy modes of Internet Explorer, Mozilla Firefox, Google Chrome, and Safari. Local shared objects created in privacy are discarded at the end of the session. Those created in a regular session are also not accessible in privacy mode.[28][29]

Third-party software


Viewers and editors

Software Developer Platform Abilities First public release Latest stable version License
Read Write Format
.minerva (GitHub) Gabriel Mariani Web platform Yes Yes AMF0/AMF3, JSON ~2008-07-15 (1.5.1) 4.1.1 (2015-01-10) BSD
.sol Editor Alexis Isaac Windows Yes Yes AMF0 Feb. 2005 (2005-02-21) MPL
SOLReader Alessandro Crugnola Windows Yes No AMF0/AMF3 2007-10-25 1.0.0 (2007-10-25) ?
FlashDevelop Mika Palmu, Philippe Elsass Windows Yes No AMF0/AMF3 2009-06-14 (3.0.0) 4.4.0 (2013-04-18) MIT
SolVE Darron Schall Windows, macOS Yes Yes AMF0 Nov. 2004 0.2 (2004-10-15) CPL

Libraries and frameworks

Software Developer Abilities First public release Latest stable version License
Read Write Format
Dojo Toolkit Dojo Foundation No Yes AMF0/AMF3 (in browser via Flash) 2004 1.9.0 (2013-05-01) BSD, AFL
PyAMF (GitHub/PyPI) Nick Joyce Yes Yes AMF0/AMF3 2007-10-07 0.8.0 (2015-12-17) MIT
s2x Open Source Flash Aral Balkan Yes Yes AMF0, XML Dec. 2003 0.75 (Dec. 2003) Freeware


Software Developer Platform First public release Latest stable version License
PrivacyScan SecureMac.com, Inc. macOS 10.6 - 10.10 2012-01-30 1.5 Shareware
Cookie Stumbler WriteIt! Studios Ltd. macOS 10.8 - 10.9 2011-04-01 2.1.2 Shareware
Cookie SweetP Productions macOS 10.6 - 10.10 2011 4.3.2 Shareware
Safari Cookies SweetP Productions macOS 10.5 - 10.10 2009-04-12 2.0 (2014-10-27) Freeware
MAXA Cookie Manager Maxa Research Windows ? 5.3 (2011-12-11) Shareware
Click&Clean Vlad & Serge Strukoff Windows, macOS, Linux, BSD, Firefox add-on 2010-01-23 ( 4.1 (2013-03-16) MIT
CCleaner Piriform (company) Windows ? ? Freemium

See also



  1. ^ a b "What are local shared objects?". Security and privacy. Adobe Systems. Archived from the original on 2010-05-29. Retrieved 2007-12-05.
  2. ^ "When the cookies crumbled, so did your web anonymity". The Guardian. 2014-10-04. Archived from the original on 2023-06-05. Retrieved 2023-12-28.
  3. ^ "ActionScript Documentation Reference for Adobe Flash Platform". Adobe Systems. 2011-08-22. Retrieved 2011-09-02.
  4. ^ "What Are Third-Party Local Shared Objects?". Security and privacy. Adobe Systems. Archived from the original on 2010-05-29. Retrieved 2011-08-15.
  5. ^ "How to disable third-party local shared objects". Support. Adobe Systems. Retrieved 2011-08-15.
  6. ^ Kirk, Jeremy (2009-08-11). "Study: Adobe Flash cookies pose vexing privacy questions". Network World. Network World, Inc. IDG News Service. Archived from the original on 2014-04-04. Retrieved 2009-04-10.
  7. ^ Cohn, Michael (2005-03-15). "Flash Player Worries Privacy Advocates". InformationWeek. UBM Techweb. Retrieved 2007-12-05.
  8. ^ Singel, Ryan (2009-08-10). "You Deleted Your Cookies? Think Again". Wired. Condé Nast Digital. Retrieved 2009-08-22.
  9. ^ Vega, Tanzina (2010-09-21). "Code That Tracks Users' Browsing Prompts Lawsuits". New York Times. Retrieved 2011-05-05.
  10. ^ "Part 2: Security, confidentiality, traffic and location data, itemised billing, CLI and directories" (PDF). Guidance on the Privacy and Electronic Communications (EC Directive) Regulations 2003 (3.4 ed.). United Kingdom: Information Commissioner’s Office. 2006-11-30. Retrieved 2011-05-05.
  11. ^ "Confidentiality of communications". Guide to the Privacy and Electronic Communications Regulations. United Kingdom: Information Commissioner’s Office. Archived from the original on 2011-02-24. Retrieved 2011-05-05.
  12. ^ James Temple (2010-01-29). "All eyes on online privacy". San Francisco Chronicle. Retrieved 11 February 2011.
  13. ^ Donald Melanson (2010-12-04). "FTC says it's talking to Adobe about the problem with 'Flash cookies'". Engadget. Retrieved 11 February 2011.
  14. ^ "Global Storage Settings panel". Flash Player Help. Adobe Systems. 2009-07-14. Retrieved 2011-05-05.
  15. ^ "Website Storage Settings panel". Flash Player Help. Adobe Systems. 2009-07-14. Retrieved 2011-05-05.
  16. ^ "Clear Flash Cookies – Add-ons for Firefox". Firefox Add-ons. Mozilla. November 20, 2017. Retrieved 2018-09-29.
  17. ^ "Adobe - Flash Player : Settings Manager". Flash Player Help. Adobe Systems. 2012-04-14. Retrieved 2012-04-14.
  18. ^ "Microsoft Announces Availability of Internet Explorer 8". PR Newswire. Redmond, Washington: PR Newswire Association LLC. 2009-03-19. Archived from the original on 2009-03-23. Retrieved 2011-05-05.
  19. ^ "Deleting "Flash Cookies" Made Easier". IEBlog. Microsoft Corporation. TechNet Blogs. 2011-05-03. Retrieved 2011-05-05.
  20. ^ a b Imbert, Thibault (2011-03-07). "Introduced Flash Player 10.3 beta!". Adobe AIR and Adobe Flash Player Team Blog. Adobe Systems. Adobe Blogs. Retrieved 2011-05-05. Integration with browser privacy controls for managing local storage – Users will have a simpler way to clear local storage from the browser settings interface – similar to how users clear their browser cookies today.
  21. ^ Huang, Emmy (2011-01-12). "On Improving Privacy: Managing Local Storage in Flash Player". Adobe Flash Platform Blog. Adobe Systems. Adobe Blogs. Retrieved 2011-05-05. Representatives from several key companies, including Adobe, Mozilla and Google have been working together to define a new browser API (NPAPI ClearSiteData) for clearing local data, which was approved for implementation on January 5th, 2011. Any browser that implements the API will be able to clear local storage for any plugin that also implements the API.
  22. ^ a b Mike Beltzner (2011-01-13). "Bugzilla entry 625495 - Clear Adobe Flash Cookies (LSOs) when Clear Cookies is selected in the Privacy > Custom > Clear History". Retrieved 2011-09-28. Change to the "on close" firefox behavior to use the new NPAPI ClearSiteData API.
  23. ^ a b Mike Beltzner (2011-01-13). "Bugzilla entry 625496 - Clear Adobe Flash Cookies (LSOs) when Cookies is selected in Clear Recent History". Retrieved 2011-09-28. Change to the "clear recent history" firefox behavior to use the new NPAPI ClearSiteData API.
  24. ^ Claudio Fontana (2011-07-17). "Bugzilla entry 672107 - Add configuration option to treat web cookies and flash shared local objects (LSOs) differently; destructive upgrade from older Firefox versions". Retrieved 2011-09-28. Loss of data on upgrade bug report, feature request for treating HTTP Cookies and Flash Local Shared Objects differently.
  25. ^ "All my saved games are gone". 2011-06-30. Retrieved 2011-09-28. Kongregate discussion about users losing data as a result of the new browser behavior.
  26. ^ "Mozilla support question: How do I stop "delete cookies" from deleting saved games of a flash based game?". June 2011. Retrieved 2011-09-28. Mozilla support question and follow-ups: How do I stop "delete cookies" from deleting saved games of a flash based game?
  27. ^ Claudio Fontana (2011-07-11). "firefox flash LSO revert patch". Retrieved 2011-09-28. Third party patch to revert the firefox cookie semantic change
  28. ^ Huang, Emmy (2011-01-12). "On Improving Privacy: Managing Local Storage in Flash Player". Adobe Flash Platform Blog. Adobe Systems. Adobe Blogs. Retrieved 2011-05-05. The ability to clear local storage from the browser extends the work we did in Flash Player 10.1, which launched with a new private browsing feature integrated with the private browsing mode in major browsers, including Google Chrome, Mozilla's Firefox, Microsoft's Internet Explorer, and Apple's Safari.
  29. ^ Betlem, Paul (2010-06-10). "Flash Player 10.1 Now Available for Windows, Mac, and Linux". Adobe AIR and Adobe Flash Player Team Blog. Adobe Systems. Adobe Blogs. Archived from the original on 2011-05-11. Retrieved 2011-05-07.