content: It is a closed-source plugin, not part of WEB-standards (HTML, JS, CSS, ...). Also, it has proven over the years to be full of bugs, a CPU hog, create accessibility nightmares and the cause of severe vulnerabilities that might have been used by malware to damage users (and it was used by the FBI too to de-anonymize TOR users). Since it is a plugin it is beyond the sandbox and security checks of the browser, in-fact it can pretty much access directly your hardware (webcam, microphone, network card, etc etc) and its apparently interminable list of bugs can be used to run arbitrary code on your machine. If you are still using Flash i strongly suggest to disable it. If you still use it for some, trusted, websites, install some extension (Flashcontrol on Chrome for instance) to only let white-listed websites use it.