Java has so many security issues, that it has it's own security settings.
Recently (in Java 7.51) Oracle made them more stringent. Just ask the owners of the sites you visit to comply to Oracles wishes and properly sign their applications.
In the meantime http://www.java.com/en/download/help/java_blocked.xml provides a work-around.
Kees
I use a Dell desktop and an ASUS laptop, both running Windows 7. Recently my Firefox has begun blocking a couple of Java-using sites that I visit often. A pop-up window says that my security settings have blocked an unsafe application. (One is the Quadcam on the University of Illinois campus in Champaign, the other is Sky & Telescope's Sky Chart. Neither has ever shown any signs of villainy in the past). I have studied the Tools/Internet Options box and can't find anything that seems applicable to the problem.
I experienced the same blockage in IE8, and it persisted even when I turned the security settings down (to medium, as low as they would go), and temporarily turned off my AVG protection and rebooted the computer. I allowed pop-up windows. Nothing worked. And the warning, even though it has a button labeled "ignore", does not let me override it and proceed anyway. It thinks that "ignore" means that it should ignore me, so it does.
Any ideas what is causing the blockage, why it happens both in Firefox and IE8 with AVG turned off, and how to get around it?
Note: I have Malwarebytes and Spybot Search & Destroy on my computer, but I am under the impression that they only come when called, and are not always active, so they shouldn't be the problem. Am I correct in this assumption?
NTG

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic