HellfireHD - 3:10 pm on Mar 12, 2013 (gmt 0)
I've had hits from over 40 IP addresses in the past 30 days all using this same User Agent.
Looking at the Apache project, it doesn't really make sense that it would be hitting the site so I started down the same path as thetrasher, looking for source code. Indeed, the Apache project DOES NOT use that user agent string while the Ararat Synapse library does.
Since it is a library I suspect many projects use it and are effectively hiding behind it. Indeed, this search on Ohloh shows exactly that: [goo.gl...]
At this point I don't think it will be effective to block the IP Addresses. The hits in my logs all come in blocks ranging from 6-30 hits and then don't appear to come back. (They might though, I'm only analyzing the past 30 days.) I am considering issuing a 403 for that user agent.