first, no security program have 100% detection.
toolbar crap and browser hijackers are not virus as they usually come bundled with programs you download
and often installed when just clicking, next, next, next …and not reading what the install info say
some of this crap may be detected by avast if PUP scan is turned on…PUP scan is default off
PUP = not a virus/Possible Unwanted Program
run AdwCleaner…click delete…post log here
you find it here. http://forum.avast.com/index.php?topic=53253.0
also run a quick scan with malwarebytes from same guide…