So I did a search and found an old thread
I remembered that had directions for modifying the hosts file. I downloaded a modified hosts file that CubeDude linked to in this thread
. I added a few specific URLs to the file, then followed the directions that Brad gave, replaced the old hosts file with the modified one, ran "lookupd -flushcache" in Terminal, and nothing seems to have happened. There are still ads on all the pages I go to and I can still access the sites that I added to the file myself. What am I doing wrong?