Once I downloaded the software by clicking on the MAC link, this is what popped out:
The official Apple stance on this issue is:
If you try to open an app that is not registered with Apple by an identified developer you get a warning dialog. This doesn’t necessarily mean that something’s wrong with the app. For example, some apps were written before developer ID registration began. However, the app has not been reviewed, and OS X can’t check whether the app has been modified or broken since it was released. A common way to distribute malware is to take an innocent app and insert harmful code into it, and then redistribute the infected app.
Iconasys has not yet registered the Shutter Stream software with Apple, for a variety of reasons, and this means that you cannot open the application directly, without exclusively telling your OS that you really intend for this application to be opened. To open Shutter Stream on your Mac, you need to add Shutter Stream to your security exception list.
To add Shutter Stream to your exception list do the following:
In the Finder, locate the app you want to open.
Don’t use Launchpad to do this. Launchpad doesn’t allow you to access the shortcut menu.
Press the Control key, then click the app icon, then choose Open from the shortcut menu.
Shutter Stream 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 registered app.
To change your security settings, see, Protect your Mac from malware.