browser tag I have never seen

has msn all over it...

[macrost]

Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; .NET CLR 1.1.4322; MSN 6.1; MSNbMSFT; MSNmen-us; MSNc00; v5m)

Any one have any ideas?

Mac

[tedster]

I'm guessing MSN Explorer.

There are some logs/analysis pages in the Google index that contain this string, or at least part of it -- but I couldn't find a definitive answer on what it identifies.

[hartlandcat]

Some ISPs add a bit at the end of the user agent string (if the user is using IE).

I quite often get this one on my site:
Mozilla/4.0 (compatible; MSIE 4.0; Windows 98; FREESERVE_IE4)