wilderness - 4:33 pm on Mar 12, 2013 (gmt 0)
I am considering issuing a 403 for that user agent.
As well you should.
In addition you should also deny the following, which has long been used as a UA for providers that cache your files.
("Begins with" and "ends with")
any other slight variation of same.
There's not much difference between these types of UA's and blank UA's.