Together with the announcement of Snow Leopard's price and availability yesterday at the WWDC, Apple announced the immediate release of Safari 4, which had been previously available in a beta version. Safari (available here or via Software Update) includes 50 (!!!) security fixes. From five fixes to CoreGraphics to four issues corrected in Safari itself to 32 fixes to WebKit (Apple's underlying rendering framework, which is used by other programs that display HTML pages, from Mail to Help Viewer to many third-party applications), this is the biggest security update (in number of discreet fixes) that we have seen in a long time. It is especially notable that this update essentially fixes just one program and a framework, unlike the general security updates that patch many elements of the operating system. We are still, however, waiting for a fix to that Java vulnerability that we reported recently.
A full list of the security fixes in Safari 4 is available here.