Avast URL malicious warning and redirect problem, need help

Hi,
Have a problem with recurrent warnings when using firefox(or explorer) and avanst blocking URL malicious site on multiple times with typical red box on bottom right of screen.

XP pro, latest firefox and avast free edition used.
The warning description of malicious site reads; ‘clikcpixelabn.com/BzzOr4op6m4ygo08dmVyPTMuOTMnv…’

I have run the avast complete system check, even run several others; adware, spybot and super antispyware to no avail. Another interesting process is the firefox on multiple occasions opening another window without doing so.

PLEASE, please help anyone. Want to getr rid of whatever this is to avoid any potential damage.

What were the webpages you were visiting when this happened? Or do they popup completely randomly?

don`t start multiple post on same subject, already posted here http://forum.avast.com/index.php?topic=64006.0