I saw this once from a Polish robot. I think the idea is to bypass UA-based blocks by having a different UA string on each request. The one I met came with a further quirk: logs tell me the robot's clock was several seconds behind my server's.
:: detour to search ::
Here's [webmasterworld.com] the resulting discussion. More recent than I thought.
In this case I'm thinking it's some kind of website downloader browser plug-in/extension with a humanoid driver, mostly because they succeeded in signing up on the forum with it. The IP is in Australia, which is plausibly okay on our forum. (They also activated the account and logged in later with a mobile UA that has no timestamp.) The timestamp format is different from the one Lucy saw, so this may not be the same animal. I'll keep an eye on them. I've not previously added a trap for rotating UAs, but I'm thinking about it.
The IP is in Australia, which is plausibly okay on our forum.
Come to think of it, I've never met an Australian robot. At least not to remember. And, when all is said and sifted, most robots infesting US-based sites ... come from US-based server farms.
For people who don't have time to pursue links: Mine, from just over a year ago, was a fully humanoid Firefox-based UA, apart from the appended timestamp. And then the discussion veered into incrediBill's header-checking routine. I knew I got it from him, but I would never have known that this was its home thread.
I tried running mpVrf2ZWrek6Mi9ZYzIwPJvc358 through a base64 converter but it didn't make sense. It's possibly (probably?) and encrypted string saying something like "Date/Time". Not entirely a joke: I regularly get attempts to authenticate on my POP3 server using the string UGFzc3dvcmQ6 which is base64 for "Password".
I'd wondered about Xing it out before posting it here in case it's a beacon of some kind - but maybe that's a little too paranoid. :D Probably the timestamp would be good enough for that anyway. Perhaps it's an encrypted node id to avoid massively parallel scrapes from being stopped by counting UA coincidences. Who knows...