I had the exact same problem and the avast process wasn't running.
What I found was that first, I am using Snow Leopard. When Apple upgraded, they made some changes to the system and how it acts. To make a long story short, the host file contains 4 addresses to start with in everyone's system. The last being
fe80::1%lo0 localhost
In most hosts files, people add after that last entry.
Therefore, you need to move it to the end. so, a hosts file example is:
##
# Host Database
#
# localhost is used to configure the loopback interface
# when the system is booting. Do not change this entry.
##
127.0.0.1 localhost
255.255.255.255 broadcasthost
::1 localhost
127.0.0.1 activate.adobe.com
127.0.0.1 practivate.adobe.com
127.0.0.1 ereg.adobe.com
127.0.0.1 activate.wip3.adobe.com
127.0.0.1 wip3.adobe.com
127.0.0.1 3dns-3.adobe.com
127.0.0.1 3dns-2.adobe.com
127.0.0.1 adobe-dns.adobe.com
127.0.0.1 adobe-dns-2.adobe.com
127.0.0.1 adobe-dns-3.adobe.com
127.0.0.1 ereg.wip3.adobe.com
127.0.0.1 activate-sea.adobe.com
127.0.0.1 wwis-dubc1-vip60.adobe.com
127.0.0.1 activate-sjc0.adobe.com
fe80::1%lo0 localhost
A quick note, if you don't want to waste time with terminal in order to edit the hosts file, download textwrangler from bare bones software (it was free). use the option to open a file, then in the pop-up enter
/etc/hosts
You can then move the fe80::1%lo0 localhost to the end and save. This will save you the hours I spent trying to fix this. Hope this helps.