I have a web site under a domain, where the main domain is using Google Analytics which sets a cookie named __utmva which is value is part binary.
As far as I can tell passing this cookie to IIS returns Bad Request (400) - "The request is badly formed.".


  1. What the hack is that cookie resposibble for?
  2. Is is allowed to pass binary values in cookies? (The request is also binary and not encoded, verified with Fiddler)
  3. If the answer for #2 is Yes, why is IIS failing and how do I fixed that?.
  • I have this exact same problem. __utmz cookie set with bad characters and making the website inaccessible to everyone who clicked on a link from an eDM. – Hiral Desai Dec 3 '12 at 2:46

This site has a nice rundown of what all the cookies do. We use Urchin (Google Analytics on speed) that uses the same/similar cookies, without issues in IIS 7.

There shouldn't be any binary data in the cookie. For that particular cookie, most of the data should just be numerics. Do you have an exmaple? Screenshot from fiddler?

Is it only affecting you? Or are others complaining about the issue too? Have you tried removing the cookie from your machin?

__utmva and __utmvb 

are NOT cookies from Google Analytics (while __utma and __utmb are GA cookies)

Actually, these are set through Response HTTP headers, not through JS.

You need to check with your development team why they set these cookies, and why there are special characters in the value of this __utmva cookie.

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