dstiles - 7:46 pm on Apr 5, 2012 (gmt 0)
I generally block IPs using a custom-built trapping system, since I use IIS.
If an IP range gets really troublesome I add the range (or part of it) to the IIS Directory Security restrictions list. I have had to do this with a few amazon ranges.
If you have htaccess (linux/unix and some IIS servers) then use that.