Apple doesn't release comprehensive software updates very often, but when it does, they contain pretty major fixes. Its latest package for Mac computers contains updates for the Safari browser as well as Mountain Lion, Apple's current operating system. Users on older machines can breathe a sigh of relief, however, as the update also provides fixes for Lion and Snow Leopard, Mac's surprisingly resilient previous two OSes.
Mac users who want to upgrade to OS X 10.8.3 need only open the Apple menu and select "Software Update," although more hands-on users can also make the upgrade manually. This will also bring Safari up to version 6.0.3, although regular Safari users will likely have already received this update.
The most important feature of the fix relates to a sizable Java vulnerability. Loading websites with malicious Java applications could cause Java to run automatically, even if users had previously disabled the program. This, of course, could lead to any number of hacks that would render even normally cautious users inert.
The rest of the issues addressed were not quite as dire, but still potentially harmful. Hackers could gain unauthorized access to Macs via compromised PDF files, bypass authentication for private directories due to weaknesses in Unicode characters and even upload destructive code via Apple's Software Update system.
One of the most interesting features of this software update is that Apple has provided it for three recent OSes instead of just two, as it usually does. While Apple has touted its Mountain Lion build of OS X, a surprising number of people are still using Lion and Snow Leopard: the builds from 2009 and 2011, respectively. [See also: Five Apple Security Myths — and the Hard Truths ]
Apple has traditionally been hesitant to support older systems, but given the number of Mac users who still have them, it may make more financial sense to invest in legacy OSes than insist that their users upgrade. The update brings Snow Leopard to 10.6.8 and Lion to 10.7.8. Legacy users should note that while these packages include all security updates, they will have to upgrade Safari separately.
10.8.3 will likely bring its own share of minor security issues to the table, but that's just how computer protection works. Hackers and IT professionals exist in a perpetual evolutionary arms race where end users are both the prey and the benefactors. Just be careful and hope that your files survive until the next generation.