Apple has not patched a serious six-month-old security vulnerability in Java. Read more
here. It's recommended that Mac users disable Java in their browsers until Apple fixes this.
Mind you, the article claims that Java isn't terribly secure for any of us; it's just particularly easy to take advantage of for unpatched versions, which includes all Macs, and lazy Windows and Linux users. So Windows and Linux folks need to make sure you're running the newest, and maybe still disable it.