The Snow Leopard update shipped alongside larger updates for Lion and Mountain Lion, OS X 10.7 and OS X 10.8.

Snow Leopard patches were unexpected. In the past, Apple has stopped serving security updates for one edition around the time it has two newer in play. If the current OS X is dubbed "n," then "n-2" support ends at the debut of "n."

In that scenario, Mountain Lion, which , serves as "n," and 2009's Snow Leopard is "n-2."

Apple has never put its support practices on paper or on its website, so customers and security experts must wait for the next round of updates to that an edition has been retired, or find out that support has been extended.

Yesterday, Apple updated both Mountain Lion and Lion with new features, improvements to existing ones, bug fixes and more than 30 patches for critical vulnerabilities.