Apple security updates
About Apple security updates
For our customers' protection, Apple doesn't disclose, discuss, or confirm security issues until an investigation has occurred and patches or releases are available. This document lists recent releases.
For more information about security, see the Apple Product Security page. You can encrypt communications with Apple using the Apple Product Security PGP Key.
Get the latest software updates from Apple
Keeping your software up to date is one of the most important things you can do to maintain your Apple product's security.
The latest version of iOS is 11.3. Learn how to update the iOS software on your iPhone, iPad, or iPod touch.
The latest version of macOS is 10.13.4. Learn how to update the software on your Mac.
The latest version of tvOS is 11.3. Learn how to update the software on your Apple TV.
The latest version of watchOS is 4.3. Learn how to update the software on your Apple Watch.
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Looks like the iMac needs a Security update, for OS X El Capitan. Here is information on this update