When installing Cloud Retailer POS we've recently witnessed the installation of Microsoft SQL 2014 as part of our process trigger AVG or Avast to block the installation.  This is a false positive.  The IPD.ALEXA.51 infection has been highly criticizedon the web as commonly occurring as a false positive with other applications as well.
You'll need to disable the virus protection temporarily to install the application.  Once done you should re-enable the virus protection and fully scan your system to ensure no legitimate threat exists on your system.