Mac users left wondering if OS X Snow Leopard's retired

OS X 10.6 users have probably seen their last core OS patches, says researcher

Apple's refusal to put into writing its operating system support policy leaves Snow Leopard users wondering whether their copy of OS X has been retired, security experts said today.

The question "Is Snow Leopard retired?" went legitimate as soon as Apple launched OS X Mountain Lion last week.

That's because Apple has always dropped security update support 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 other words, patches are provided only to the newest OS X and the one immediately preceding it. With Mountain Lion's debut last Wednesday, that informal policy -- Apple has never put its support practices on paper or its website -- means the two editions that will receive patches are OS X 10.7, aka 2011's Lion, and the brand new 10.8, or Mountain Lion.

Apple last shipped a Snow Leopard security update in May 2012.

"I would expect that Snow Leopard is toast," said Chet Wisniewski, senior security adviser at Sophos, when asked today of his expectations. "They seem to apply that 'n-2' rule [of no security updates] somewhat universally, even when it doesn't make sense."

Apple has held to the n-2 rule, although the timing of an edition's final update has varied.

Last year, Apple shipped the last OS X-wide security update for Leopard (n-2), the edition released in Oct. 2007, on June 23, 2011, almost a month before the launch of Lion (n). OS X Tiger (n-2), which appeared in April 2005, received a final security update on Sept. 10, 2009, 12 days after Snow Leopard (n) shipped.

Prior to that, Panther (n-2), or OS X 10.3, got its final update two-and-a-half weeks after the debut of Leopard (n), while OS X 10.2, aka Jaguar (n-2), saw its last patch three months before the launch of Tiger (n).

An edition's retirement isn't comprehensive. Apple has typically delivered separate security updates for four components: iTunes, Java, QuickTime and Safari for several months beyond the cut-off.

OS X security chart
Apple usually delivers the final security update for an older edition ('n-2') around the time when a new upgrade ('n') ships. (Data: Apple.)

For example, Apple updated iTunes for Leopard as recently as last month, and patched QuickTime in August 2011. (The company also shipped a security-related update for Leopard in May 2012 that did not patch any vulnerabilities but instead disabled long-outdated versions of Adobe's Flash Player, one of several moves made this spring to protect Mac users from the Flashback malware.)

The problem isn't necessarily that Apple retires each edition of OS X -- every software vendor does that -- but that it won't tell customers when it does.

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