Dear Cathy,
Dozens of people have been downloading without problems. I download CLANc myself right now with no problem. So, this is most likely something unique to her computer setup. If she is using a machine linked to some University facility, she should contact her administrators there. Perhaps they have set up some sort of firewall. Better still, she could try downloading from another machine on a different network.
Just to be sure, I hope she is not talking about the scary message that the Catalilna system gives when installing new software for the first time about the software being "malicious". When you get this you have to go into System Preferences/Security to allow installation. This only happens the first time you install a new program.