Since I have installed Java 7 update 45 on our test slaves I get the following security warning:
Running applications by UNKNOWN publishers will be blocked in a future release because it is potentially unsafe and a security risk.
This application will be blocked in a future Java security update because the JAR file manifest does not contain the Permissions attribute. Please contact the Publisher for more information.
It looks like that the .jar file(s) do not contain a permissions attribute, which would let slaves connect to the master in the future. In our case we connect slaves via Java web start.
As of now it is not a hard-blocker and you can click through and accept. But I think that this should be fixed soon.