Listen and slow down a little bit, Gert2... no need to hurry...
Of course avast! tried to change something in order to be able to check your incomming and outgoing e-mails... otherwise there is no point in having antivirus e-mail protection... right ?
Second thing... HOSTS file is nothing bad. You should have hosts file in above mentioned directory, but all those nasty things inside your hosts file, shouldn't be there.... when I say nasty things, I mean on these you mentioned before:
127.0.0.1
www.doubleclick.net127.0.0.1 ad.preferances.com
127.0.0.1 ad.doubleclick.com
127.0.0.1 ads.web.aol.com
127.0.0.1 ad.doubleclick.net
127.0.0.1 ad.preferences.com
127.0.0.1 ad.washingtonpost.com
127.0.0.1 adpick.switchboard.com
127.0.0.1 ads.doubleclick.com
127.0.0.1 ads.infospace.com
127.0.0.1 ads.msn.com
127.0.0.1 ads.swit
As I said before, you should have
127.0.0.1 localhost only inside your HOSTS file.
You shouldn't erase hosts file, just those keys mentioned above...