I also noticed it. Download.com is not a good site now. I remember I gor "default tab" instaled with CNET downloader. I initially thought it came from the software I was using. Even I uninstalled Avast assuming it's not working. But later I found it's CNET installer which is causing the trouble. From that time onwards I always download software from the actual developer's site
Initially I chose CNET because I thought they only keep SPyware Free , adware free products. But now they only providing those. It may get them few extra bucks initially but in long run they will be in loss.