@wilderness, some people hosted on shared servers don't have access to raw logs. Others are simply unaware of their existence, or how to download them.
@incrediBILL, There was a thread here a couple of years ago about this that I replied to, but even though I've looked, I can't seem to find it.
@ichthyous, What you are seeing is an artefact of AWStats. If you are able to read your raw log file, you would most probably find that whichever bots it was that visited on 10 Apr 2012 - 15:42 and 10 Apr 2012 - 15:21, they certainly had a normal user-agent, not the regex puzzle quoted by AWStats.
In my case, all the ones I have bothered to follow up have been legitimate bots, and even include Google's AdsBot. It isn't one single bot, its a whole bunch.
Bottom line, ignore it! ;)