I know this is an old question, but this process just got a lot more difficult with the most recent version of Java.
This link explains the general problem well: https://shellzero.wordpress.com/2014/01/24/how-to-fix-application-blocked-by-sec urity-settings-mac-os-x/
However, there are extra steps required to make Wordle work on a Mac, as the Wordle domain redirects to other domains when creating a Word cloud. To make it work, here are the steps (#1-3 are the same as listed on the link above).
1. Go to System Preferences (click the apple in the top left corner to get there).
2. Click the Java icon near the bottom (you probably won't be able to see this icon if you're connected to a projector as the resolution cuts out the bottom of the window).
3. When the Java Control Panel window opens, click on the "Security" tab.
4. In the "Exception Site List," add the following sites: