Local Shared Objects

Today’s poke at paranoia is brought to you by the letters L, S, and O. Together, they form the initials LSO, “Local Shared Object.”

The LSO is a data storage mechanism that originated with Adobe Flash about 10 years ago. The purpose of LSO was to allow Flash to store information on your computer about Flash movies or games that you were using in your browser. The LSO might store your game position, or your location in the movie.

The LSO is like a cookie in the browser cookie cache. However, unlike cookies, a single LSO cache is used by all browsers. Thus, if you play your Flash movie in Firefox, and then later reconnect to it with Internet Exploder, Flash will be able to reload your information stored while you were using Firefox.

About the time that advertisers and web sites began to be hammered by paranoia about cookies, and especially about 3rd party cookies, they discovered the genius of the LSO cache. The LSO data storage mechanism is almost unknown to non-technical users. “Clear browsing history,” in any of its incantations, does not touch LSO. This fact led to something dubbed cookie re-spawning.

When the browser accepts a cookie from a web site, the site may also choose to store a copy of that cookie in the LSO cache. Now, suppose you delete that cookie. The next time you are using that web site, if the cookie is not found, the site will automatically look for a copy in the LSO cache; if it finds one, it respawns or recreates the deleted cookie with the saved information.

Web developers bolted on several methods of manipulating the LSO cache in their web sites. HTML 5 formalized a methodology for this activity. Your friendly web site can now bank information about you in the LSO cache with a few lines of JavaScript on the page.

Haha! You were being so conscientious about deleting your cookies, too.

All is not lost. Newer versions of Firefox now include the LSO cache in “delete browser history,” and other browsers provide options to delete items from it, as well. If you’re feeling, well, paranoid.