14 DAY TRIAL // Matt Cutts, a Google engineer, said that Microsoft added MSNBot the same technology GoogleBot uses, a technology that includes a reverse DNS lookup followed by a forward DNS lookup.
Brent Hands, Program Manager for Live Search, confirmed it on the official blog and added that all the sites are crawled and identified by a single agent entitled MSNBot.
"After all, anyone could call themselves 'MSNBot', and proceed to be as rude and aggressive as they like. Fortunately, there is a way you can catch these impersonators. Here is how it works:
1. When you get a page view request, it specifies a user-agent and an IP address. As I described above, all requests from Live Search use a user agent starting with the word 'MSNBot'.
2. If you see the MSNBot user-agent, it's time to check the identity of the bot. Starting with the IP address (i.e. 207.46.98.149), you can use reverse DNS lookup to find out the registered name of the machine.
3. Once you have the host name (in this case, livebot-207-46-98-149.search.live.com), you can check that it really is coming from Live Search. The name of all live search crawlers will end with 'search.live.com'. If the name doesn't end with 'search.live.com', you know it's not really our crawler.
4. Finally, you need to verify that the name is accurate. In order to do this, you can use Forward DNS to see the IP address associated with the host name. This should match the IP address you used in Step 2 - if it doesn't, it means the name was fake."