not2easy - 3:26 am on Feb 23, 2012 (gmt 0)
You are right, that is why I had not implemented anything although I have been trying to beat back this problem with normal means for months. I was very concerned about performance, blocking over 500 domains by referer, and that was only the multiple entries. My last look in GWT told me I had better do something so I started looking for what would work. The more I read, the less I could see what would help. Trying to decide how to stop it I kept running into a wall. "That won't work because.." I took a look at today's access logs and see a few unusual entries after the update but 403s where I was trying to put them in several instances already so I am encouraged. That one new line is making a difference. I will look closely for the next few weeks to see if there is another detail that might help. I have much more reading to do.
Thanks to all who helped.