avast doesn't block web sites unless you specifically have it block them, it isn't a firewall.
I can access all three of those sites with no problems obviously the last one or I couldn't answer this.
I suggest you check your HOSTS file as commonly if you can't access security sites it could be it has been tampered with. I can see no reason why the other two would be blocked using the HOSTS file.
HOSTS file redirect - 127.0.0.1 check your HOSTS file using notepad or a text editor of your choice, C:\WINDOWS\system32\drivers\etc\hosts or do a search for HOSTS to find it if not there. http://en.wikipedia.org/wiki/Hosts_file
You would be looking for avast.com as an entry with 127.0.0.1.
David, in Note Pad I have opened this Hosts file and the details are as under:
# Copyright (c) 1993-1999 Microsoft Corp.
# This is a sample HOSTS file used by Microsoft TCP/IP for Windows.
# This file contains the mappings of IP addresses to host names. Each
# entry should be kept on an individual line. The IP address should
# be placed in the first column followed by the corresponding host name.
# The IP address and the host name should be separated by at least one
# Additionally, comments (such as these) may be inserted on individual
# lines or following the machine name denoted by a '#' symbol.
# For example:
# 22.214.171.124 rhino.acme.com # source server
# 126.96.36.199 x.acme.com # x client host
For Avast 4.8 Home Edition I am currently using:
Build: Jul2008 (4.8.1229)