Error: Cisco WebEx addon is damaged while installing

I had this problem too. What you need to do before running the installation is go to System Preferences>Security & Privacy and, in the 'General' tab, go to the bottom section ("Allow apps downloaded from:") and select the option "Anywhere". Now run the installation, you'll be prompted to verify if you want the installation process to continue.

For security purposes, after finishing the installation, go back to Security & Privacy in System Preferences and change back the option in the "Allow apps downloaded from:" section of the 'General' tab to either "Mac App Store and identified developers" or "Mac App Store", according to your preference.

Hope this helps.