I used Mountain Lion since the earliest beta's, and it is true. By default it only runs signed applications (and applications from the app store are, by requirement signed). Running an unsigned application will give an error. However, you *can* disable this in the security settings, so that it will run every application.
Posted Aug 11, 2012 20:05 UTC (Sat) by Kit (guest, #55925)
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That's not really accurate, though.
It only prevents applications downloaded from the Internet that are /completely/ unsigned (and only if the program that did the downloading marked them as such). Self signed apps will receive a scary warning, but can still be opened, while apps signed with an Apple-provided certificate will work fine (doesn't matter if they're distributed via the App Store).
This means that already-run apps will work just fine, as would apps that are acquired via physical media (such as CD/DVD/flash sticks).
The reporting has done a fairly poor job of explaining exactly what it restricts and how it functions, unfortunately.