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Which seems to be following Googles lead by using dns lookups as a way to identify the real bot verses someone trying to spoof them.
This is only for MSNBOT/1.0 so far not the MSNBOT-media and other variants from Microsoft.
MSNBOT include an extra Header "From" with a value "msnbot(at)microsoft.com" which can also help weed out spoofers.
I seem to recall that 1.0 was the MS image bot?
As previously mentioned in another thread
( [webmasterworld.com...] ), I have severe problems of communication with the many MS bots.
Yesterday, I have 1.0 crawling with the same UA from three entirely different ARIN ranges.
220.127.116.11 (APNIC denied)
msn-dude informed us a while back that MS was sorting out their bot identities and UA's however these inconsistecies seem to just add more confusion.