Flash cookie

A Flash cookie, also known as a local shared object, is a text file that is sent by a Web server to a client when the browser requests content supported by Adobe Flash, a popular browser plug-in.

Flash cookies are commonly used in website advertisements and videos. Like HTTP cookies, Flash cookies store information on the end user's computer. The information allows a website to recognize the client's browser when it returns. Flash cookies sometimes contain the same information that HTTP cookies contain, but they also store information specific to Flash such as the place where the user's video stopped playing or an animated banner advertisement stopped rotating. Local shared object files have an .sol file extension.

Unlike HTTP cookies which are stored with the browser's files, Flash cookies are stored in a separate Adobe file and may have to be managed and deleted separately through Adobe Flash player settings. Many end users are unaware that Flash cookies exist and have no idea that when they delete their browser's HTTP cookies, Flash cookies could remain unaffected and be used to recreate deleted HTTP cookies. The recreation process, which is called respawning, is extremely controversial because it facilitates cross-browser tracking and poses privacy concerns when the use of Flash cookies is not disclosed in a website's privacy policy.

To deal with potential abuses of local shared objects, Adobe has made changes in Flash to discourage Flash cookie respawning and has provided information on their website about Flash cookie management. The company has also partnered with major browsers to make it possible for end users to manage local shared object files through browser settings with an additional application program interface (API).