Live Search is testing an update to MSNBot, which may show up as a new crawler name in your server referrer logs. The new crawler user agent string will appear as: msnbot/2.0b (+http://search.msn.com/msnbot.htm)
You’ll still see the current version msnbot/1.1 (+http://search.msn.com/msnbot.htm) as Live Search’s primary user agent. We intend to ensure that any robots exclusion protocol you are using is respected. As such, you don’t need to update your Robots.txt file. We plan on crawling at a slow speed during the tests with the updated version, reports Live Search Webmaster Center Blog.