The safest place to get apps for your Mac is the App Store. Apple reviews each app in the App Store before it’s accepted and signs it to ensure that it hasn’t been tampered with or altered. If there’s ever a problem with an app, Apple can quickly remove it from the store.
If you download and install apps from the internet or directly from a developer, macOS continues to protect your Mac. When you install Mac apps, plug-ins, and installer packages from outside the App Store, macOS checks the Developer ID signature to verify that the software is from an identified developer and that it has not been altered. By default, macOS Catalina and later also requires software to be notarized, so you can be confident that the software you run on your Mac doesn't contain known malware. Before opening downloaded software for the first time, macOS requests your approval to make sure you aren’t misled into running software you didn’t expect.
Running software that hasn’t been signed and notarized may expose your computer and personal information to malware that can harm your Mac or compromise your privacy.
By default, the security and privacy preferences of your Mac are set to allow apps from the App Store and identified developers. For additional security, you can chose to allow only apps from the App Store.
In System Preferences, click Security & Privacy, then click General. Click the lock and enter your password to make changes. Select App Store under the header “Allow apps downloaded from.”
If your Mac is set to allow apps from the App Store and identified developers, the first time that you launch a new app, your Mac asks if you’re sure you want to open it.
An app that has been notarized by Apple indicates that Apple checked it for malicious software and none was detected:
OS X Mountain Lion is available now as a download from the Mac App Store. Just click the Mac App Store icon in your dock, purchase Mountain Lion, and follow the onscreen instructions to install it. Mountain Lion will not only make your Mac work better, it also makes your Mac work even better with your iPhone, iPad, and iPod touch. Because it comes with iCloud, your mail, calendars, contacts.
Prior to macOS Catalina, opening an app that hasn't been notarized shows a yellow warning icon and asks if you're sure you want to open it:
If you have set your Mac to allow apps only from the App Store and you try to install an app from elsewhere, your Mac will say that the app can't be opened because it was not downloaded from the App Store.*
If your Mac is set to allow apps from the App Store and identified developers, and you try to install an app that isn’t signed by an identified developer and—in macOS Catalina and later—notarized by Apple, you also see a warning that the app cannot be opened.
If you see this warning, it means that the app was not notarized, and Apple could not scan the app for known malicious software.
You may want to look for an updated version of the app in the App Store or look for an alternative app.
If macOS detects that an app has malicious content, it will notify you when you try to open it and ask you to move it to the Trash.
Running software that hasn’t been signed and notarized may expose your computer and personal information to malware that can harm your Mac or compromise your privacy. If you’re certain that an app you want to install is from a trustworthy source and hasn’t been tampered with, you can temporarily override your Mac security settings to open it.
In macOS Catalina and macOS Mojave, when an app fails to install because it hasn’t been notarized or is from an unidentified developer, it will appear in System Preferences > Security & Privacy, under the General tab. Click Open Anyway to confirm your intent to open or install the app.
The warning prompt reappears, and you can click Open.*
The app is now saved as an exception to your security settings, and you can open it in the future by double-clicking it, just as you can any authorized app.
macOS has been designed to keep users and their data safe while respecting their privacy.
Gatekeeper performs online checks to verify if an app contains known malware and whether the developer’s signing certificate is revoked. We have never combined data from these checks with information about Apple users or their devices. We do not use data from these checks to learn what individual users are launching or running on their devices.
Notarization checks if the app contains known malware using an encrypted connection that is resilient to server failures.
These security checks have never included the user’s Apple ID or the identity of their device. To further protect privacy, we have stopped logging IP addresses associated with Developer ID certificate checks, and we will ensure that any collected IP addresses are removed from logs.
In addition, over the the next year we will introduce several changes to our security checks:
*If you're prompted to open Finder: control-click the app in Finder, choose Open from the menu, and then click Open in the dialog that appears. Enter your admin name and password to open the app.
Even though eyes are on next week’s Worldwide Developers Conference, which is rumored to usher in the next major update to OS X, Apple hasn’t stopped supporting its current version. The company on Tuesday released Mac OS X 10.8.4, bringing numerous fixes and improvements.
Among the changes in the latest Mountain Lion update are improved compatibility with certain enterprise Wi-Fi networks, better Microsoft Exchange compatibility in Calendar, a fix for issues with FaceTime calls to non-U.S. phone numbers, and—to cries of joy heard round the world—a solution for an issue where iMessages might show up up out of order in Messages.
A new version of Safari, 6.0.5, is included in the download as well; Apple says it improves stability for some websites with chat features and games. (Not that anybody uses the Web for chatting or playing games, right?)
Additionally, Calendar birthdays should no longer appear incorrectly in certain time zones, VoiceOver compatibility for text in PDFs should be better, and an issue where the desktop background picture wasn’t correctly preserved after restart should be fixed. There a number of other tweaks and enhancements, as detailed in Apple’s support knowledge base document.
As per usual, the OS X update also features a number of security fixes, making it recommended for all OS X Mountain Lion users; the included Safari 6.0.5 likewise has its own security updates. Users of earlier versions of OS X can download Security Update 2013-002 to receive the same patches.
Mac OS X 10.8.4 is available as a free download via the Mac App Store. As of this writing, it wasn’t yet available as an update from Apple’s support downloads site.
Updated at 1:40 p.m. PT with further details about security patches.