how to delete adware, etrecheck
MacBook Pro, OS X Mountain Lion (10.8.2)
Try clicking "Remove".
Or download and run MalwareBytes for Mac http://www.adwaremedic.com/index.php
Or try Apples instructions for manual removal Stop pop-up ads in Safari - Apple Support
And finally uninstall Avast, it's slowing your computer down and does absolutely nothing helpful.
how to delete adware, etrecheck