Flash is a program that allows you to see animation and interact with websites. This plugin is necessary to use the Arcade, but since many security issues float around its use we closed the Arcade. I have not had a chance but I am looking at HTML 5 games as a replacement as it will offer good competition.
I figured this will be the problem with most Users hence going with HTML5 games will be best since it works on typical browsers without the need to install anything. The same main issues still remains - cheating, but I will keep that for; Creative Ways To Stop Users From Hacking Client-side Games.