BREAKING NEWS: You can tell this update is a biggie by how tight lipped and to the point Apple is with it and also by the appearance of the words “zero day” in the text of the update notes – meaning Apple has exactly zero days to fix this one because it was discovered in the wild, likely on many if not all Macs right now – the release seems to come yesterday (today), New Zealand is +11 GMT.
This update from 9.1 to 9.1.1 prevents “drive by” exploitation of Safari for remote code execution, which IN ENGLISH means all you need to do is visit a bad guy website (or a good website somehow infected with bad guy code) and the bad guys can run arbitrary software they wrote on your machine without permission or
If your curious about computer security I recommend reading Apples sections.