If you are getting error "Book Keeper.msi is not an legimate Application or plug-in. You are not allowed to install through browser sandbox environment.
You need to follow below steps:
1. Open Quick Heal, a window will open like shown below:
2. Click on Internet & Network, you will get window like shown below:
4. Please Disable Browser Sandbox option.
5. Now install Book Keeper again, you will not face the same issue again.