How do I fix a Java security error?

Do you get the following error when attempting to use MySource Matrix?

Java Error 

Oracle released Java 7 Update 51 on January 14th. As part of the installation, the Java security level is set by default to High. With this security setting, self-signed and unsigned applets are blocked from running.

This page has a good explanation on how to fix the error 

Even though the example is on a Mac it works for PC too. Most people affected don't change the slider referred to in the link but add their site's URL to the exception list, that seems to work best.

Users should contact their your local IT staff before applying this fix because it does involve changing security settings.