rowan194 - 2:01 am on Jun 30, 2010 (gmt 0)
Here are the 3 UAs I've found so far-
Casper Bot Search
dex Bot Search
Mozilla/4.76 [ru] (X11; U; SunOS 5.7 sun4u)
I'm 403'ing anything presenting this user agent, then a script which runs every 15 mins adds a firewall rule for that IP. (They won't even be able to connect to the server, let alone request anything)
I've counted 268 unique IPs since just over a week ago, so I wouldn't be surprised if the requests are coming from compromised boxes.