I just come to know by lots of guys that Java Applet is vulnerable.Either you have misunderstood or you were misinformed. Java applets can be a vulnerability. They aren't themselves vulnerable as far as I know.
what is the workaround for this Security issues ?Install the latest version of Java.
Can i use any RSA Certificate to prevent attacks ?Of course not. Certificates don't prevent security attacks.
Must my clients update Java to latest version on their machine ?Always.
I have a Joomla website that recently had a red puzzle shape java applet appear to the left of my domain address. The layout had completely messed up for no apparent reason and I was worried that it was somehow related to Java. When I clicked on this red icon and selected to activate a Java plugin, my computer was almost instantly infected with a trojan virus that disabled my internet and ability to even run my anti virus software or task manager. I had to reboot in safemode just to get rid of the thing. Does anyone know anything about this and if this could be the result of a hack attack on my site? Could the layout problems be resulted to this Java problem????
Its not a Java problem, you were just the victim of internet abuse. You don't install Java by clicking on red icons, you either install it through Java.com or you get automatic updates from the Java already installed. So congratulations, you are a victim of the web. Install better protection software and use a better internet browser.
I don't believe it's the applets that are vulnerable. It's the Java Runtime Environment (or JRE). This is what the end-user runs on their computer in order to run Java applets. If a malware author finds a security hole in the JRE then unsuspecting people who visit their malware-infected website could unknowingly run the bad applet. They can allow viruses to be installed on the end-user's computer without them ever knowing. Users should keep Java up-to-date and run a patched anti-virus. It my personally believe, move away from using Java if possible.