Sian
In OS X 10.11 and earlier you can prevent these warnings by changing your privacy settings to allow non-certified programs to run. In your System Preferences, go to Security > Privacy > General and set "Allow Applications downloaded from" to "Anywhere".
If you are running OS X Sierra (OS X 10.12) then the steps have slightly changed. Please see the following article for more information.
SUMMARY
When trying to download and install our software on OS X you may receive an error message that reads "... can't be opened as it is from an unidentified developer". This article will explain what to do in this situation in order to continue with the installation.MORE INFORMATION
The default security settings on OS X will only let a user install or run programs that are certified/authorized by Apple. When you try to install or run a program from The Foundry you may get a warning saying that the program "cannot be opened as it is from an unidentified developer" and the program will not run.