In the latest set of security updates for OS X, Apple has included a new version of Safari for users still running OS X 10.6 Snow Leopard. The last official release of Safari for Snow Leopard was version 5.1.7, which addressed several bugs in the WebKit framework that could allow maliciously crafted Web sites to execute code locally on a system. Since then there had been no updates for Safari 5; however, if you are using Snow Leopard and have installed the latest update you will see Safari is now at version 5.1.8.
As noted by Josh Long on Intego's Mac Security Blog, Apple had apparently stopped issuing new versions of Safari for Snow Leopard, leaving users with a number of vulnerabilities that have since been patched in Safari 6 for Lion and Mountain Lion.
In the latest security updates, Apple makes no specific mention of Safari or some of its core components like WebKit, so it is unknown what features were changed. One issue Apple did address was how the system handled Java Web Start files being able to execute once downloaded since the system identified them on the Safe File list, so it is possible Apple included small changes in this or a similar area.
Another possibility is the changes in Safari 5.1.8 could mirror those in Safari 6.0.3, which responded to yet another set of potential code-execution flaws in the WebKit framework.
Overall, while Safari did get updated in this latest round of security patches, the update doesn't bring any notable new features from a user perspective. As with most minor updates it is likely just a bug fix or compatibility update, but it may show Apple stepping up efforts to improve security.