Does your web site use Flash? Flash is frequently used to serve animations, videos, adverts and interactive multimedia content. In order to work it depends on your web site visitor having a browser with the necessary plugin installed. Time was when you could fairly much rely on that. In fact, so widespread was Flash that up until a few months ago YouTube depended on it. However, due to a poor history of security vulnerabilities, and with the growth of HTML5 (which is the alternative to Flash that YouTube now defaults to), the days of Flash seem to be numbered. So maybe now is the time to take Flash off your web site! (If you are not sure whether your site uses Flash, look for the HTML
<object> tag in the source code referencing a *.swf file. Or, perhaps easier, disable the Flash plugin in your browser, and see if your website performs correctly).
Fortunately there is a fairly easy and reliable way to convert your existing Flash files to HTML5 using Google’s free Swiffy utility. Check out https://developers.google.com/swiffy/!