The download speed is probably just a matter of download speed.
What is the downloaded filesize?
As for it freezing -- maybe that is Norton, assuming calibre is a virus just because it connects to the internet. No kidding, so do browsers.
calibre also checks for updates.
I agree with theducks and JSWolf -- Norton is not a very good choice for an antivirus.
Make sure calibre is not being blocked by Norton -- preferably uninstall and replace with any of several good, free antiviruses, or at least make sure calibre is on the exceptions list.