I installed IE9 in a Windows 7 virtual machine, and was surprised to see this user agent:

Mozilla/5.0 (compatible; MSIE 9.0; Windows NT 6.1; Trident/5.0; BOIE9;ENUSMSNIP)

In particular, the last two keys BOIE9 and ENUSMSNIP look very spammy. I'm used to seeing toolbars and add-ins register themselves at the end of the user agent like that, but this is on a virgin install of Windows 7 with no other software.

They're defined in the registry here:

HKCU\Software\Microsoft\Windows\CurrentVersion\Internet Settings\5.0\User Agent\PostPlatform

That key has a value of IEAK, which is apparently the Internet Explorer Administrators Kit which according to Microsoft sends a custom user agent string.

But why?

I'm guessing that BOIE9 is stands for "Bing on IE9". It's the only active Add-On:

As for ENUSMSNIP, I'm at a loss. My guesses are:

• ENUS = Locale, which for me is EN-US ("US English")
• MS = Microsoft
• NIP = ???

I tried changing my locale to EN-GB, but the user agent didn't update nor did the registry. So it appears it's only at the time of install that it matters (if I'm even right about ENUS).

Does anyone know what these two user agent keys represent?

Or, care to share what your IE9 user agent is, and maybe we can piece it together ourselves?