1. Network Shield (not a firewall) monitors for these type of exploits which are often rampant and if avast is blocking them it isn't a reason for worry. For the most part even if you didn''t have the network shield provided you have kept your Operating System up to date then these exploits can't work, not that it stops them trying.
Do you have a firewall?
2. Until you register and enter the registration key (free) then you have full unrestricted use for 60 days. avst needs to know how many active users they have and where they are so they can estimate the server loads to support updates, downloads etc.
Once you register you have 14 months of free Virus Signature Updates then you will need to register again for a further 14 months free VPS updates, very reasonable I feel for an excellent anti-virus.
avast! 4 Home Registration
