OS X El Capitan: The Missing Manual

Other Ways to Get Mac Software

In general, new programs arrive on your Mac via one of two avenues: as a download (whether from the App Store or not), or on a CD or DVD.

Downloading Compressed Files

Programs you download from the web (not the App Store) generally arrive in a specially encoded, compressed form (Figure 5-2). And unless you’ve changed the settings, they arrive in the Downloads folder on your Dock.

FREQUENTLY ASKED QUESTION: What’s with the Big “Duh”?

So I double-click an Excel document, and the Mac asks me: “You are opening Microsoft Excel for the first time. Do you want to continue?” Well, HELLO! I double-clicked the icon, didn’t I? Does Apple think I’m some kind of idiot?

It’s not you Apple is worried about. It’s the silent parade of evil hackers, lurking out there in Internet Land, waiting for the right moment to bring down the Mac.

See, spyware authors have to be sneaky about how they install their stuff on your computer. You wouldn’t be so stupid as to double-click an application called Spyware Installer™, of course. So the spyware tricks you into running its installer. In the Windows world, it commandeers a certain document type (like MP3 or JPEG), reassigning it to its installer. You innocently double-click some document, but an unanticipated program opens—and you’ve just opened Pandora’s box.

In OS X, that can’t happen. When you double-click some document that opens a program for the first time, this dialog box appears, just to let you know what’s about to happen. ...