chrome opens undesired webpage

Hi pals,

Since a month, when i’m reading a webpage, then i click on any place on the page… sometimes the browser opens a undesired webpage in a new tab: GUIACONSUMIDOR.COM. Then i try to close that new tab, but a popup opens. When i close this popup then GUIACONSUMIDOR opens again. At the second time i close the page finally i get it closed.

Please, anyone can help me? Maybe could it be a trojan?
I have
Windows 7 Home Premium
Chrome 20.0.1132.57
Avast Internet Security 7

any help will be appreciated
(sorry for my bad english)

Regards
Jorge Campos

follow this guide and attach (not copy and paste) the logs requested
http://forum.avast.com/index.php?topic=53253.0