An application may be automatically opened two ways: either by opening a document that is associated with the application or by clicking a link (URL) in a webpage or document.
Opening an application manually or automatically
You can manually open an application, such as by clicking its icon in the Dock; or the application may open automatically, such as when you click a link or open a document associated with the application.
For example: You open Safari manually if you double-click its icon in the Applications folder or click its icon in the Dock. Safari opens automatically if you open a document such as "mypage.html", or click an "http://" link that's in a document.
How does Mac OS X know which application to open automatically?
This is done by association (or "mapping"). Mac OS X associates each major type of document (such as text, pictures, movies, and webpages) and each major type of link (such as "http://") with a particular application. When you open a document or click a link, it automatically opens in the associated application. If you encounter a document or link type that is not associated with an application installed on your computer, Mac OS X asks you to choose which application to open it with. In the example, webpages (.html) and Web links ("http://") are both associated with Safari by default.
Tip: You can change the application associated with a type of document in the Info window. In some cases you can use application preferences, such as the Default Web Browser preference in Safari.
A warning for new applications
When you open an application manually, you are making an explicit choice to do so. But when you open a document, it may not be clear which application will be used. If you click an untrustworthy link, it may try to automatically open a downloaded application designed to cause harm to the system. The feature provided by Security Update 2004-06-07 alerts you if an application that is automatically opening hasn't already been opened, either manually or by consent to this warning dialog:
Opening an application manually or automatically
You can manually open an application, such as by clicking its icon in the Dock; or the application may open automatically, such as when you click a link or open a document associated with the application.
For example: You open Safari manually if you double-click its icon in the Applications folder or click its icon in the Dock. Safari opens automatically if you open a document such as "mypage.html", or click an "http://" link that's in a document.
How does Mac OS X know which application to open automatically?
This is done by association (or "mapping"). Mac OS X associates each major type of document (such as text, pictures, movies, and webpages) and each major type of link (such as "http://") with a particular application. When you open a document or click a link, it automatically opens in the associated application. If you encounter a document or link type that is not associated with an application installed on your computer, Mac OS X asks you to choose which application to open it with. In the example, webpages (.html) and Web links ("http://") are both associated with Safari by default.
Tip: You can change the application associated with a type of document in the Info window. In some cases you can use application preferences, such as the Default Web Browser preference in Safari.
A warning for new applications
When you open an application manually, you are making an explicit choice to do so. But when you open a document, it may not be clear which application will be used. If you click an untrustworthy link, it may try to automatically open a downloaded application designed to cause harm to the system. The feature provided by Security Update 2004-06-07 alerts you if an application that is automatically opening hasn't already been opened, either manually or by consent to this warning dialog:
You can either open the application or cancel the attempt, which is appropriate if you don't recognize or trust the application.
Once an application has been opened, this message will not appear again for that particular application.
Applications included with your computer are considered "trusted" and will not trigger the warning panel.