lucy24 - 10:45 pm on Apr 23, 2011 (gmt 0)
Just when you thought you'd got it all figured out...
I have accidentally discovered a situation where a perfectly legitimate, law-abiding activity results in a blank user-agent string. If you want to split hairs, it's a single hyphen "-" but I think my server puts that in as a placeholder. I've never seen a genuine blank "".
I've got a png that I use as part of my signature in a small forum. The png lives in my personal www space but isn't linked from anywhere, so it doesn't get crawled. It does show up in logs in the expected form, with "viewtopic" et cetera as referrer.
Recently the Forums administrator did some stuff with the signature file at my request. Logs for the relevant time period showed a series of 403's for the png-- with blank user-agent, and a source IP that agrees with the Forums. (I specifically asked her.)
Coincidentally I use the same host, but we're not on the same server so I don't think that's relevant. Oh, and the 403-- from the blank UA lockout in .htaccess-- doesn't seem to have prevented her from fixing the sig. It may be what prevented me from fixing it, though.