BFG v1.12.4 - now requires Java 7
This bumps a few dependency versions, specifically JGit, which now requires Java 7, ending Java 6 support in the BFG. You'll get an immediatejava.lang.UnsupportedClassVersionError if you try to run BFG v1.12.4 with Java 6.
You can get the latest version of Java (currently Java 8) here:
If you really want to run with Java 6, BFG v1.12.3 is the final version you'll be able to use.