If you are running Java 6 on a Macintosh, you should run Apple's latest software update 12 released February 1st. If you have been running Java 7 you may get a notice when opening the Blocks Editor that asks you to update Java. You must run this update to use App Inventor. This issue is due to a vulnerability in Java that affects all users -- not just App Inventor users and not even just Mac users. We will continue to monitor the situation and let you know what else, if anything, you'll need to do.
Import Information about Java and App Inventor
Submitted by jeff on