See Specifying from where to obtain virus definitions.You must have a valid content license to install definition files.Symantec encourages users to rely on the full quality-assurance-tested definitions whenever possible.Ensure that you deploy Rapid Response definitions to a test environment before you install them on your network.Symantec updates Rapid Response definitions as needed.They respond to high-level outbreaks and might be made available before the Live Update definitions quality assurance process is complete.Rapid Response definitions undergo the basic quality assurance testing by Symantec Security Response.
Every 10 minutes, Symantec Brightmail Gateway polls Symantec servers to see if updates are available. I click on update now in upper right hand corner and then click on update for virus definitions. The screen runs and then says everything is up to date BUT even after rebooting the red notice stays. Updates to the Program provide bug fixes and general improvements.By default, Avast Antivirus is set to update the Virus definitions and Program automatically whenever a new version is available.The availability of a new version is checked when an Internet connection is established, and every four hours afterwards.