TSM_Hiddenfield? What is that? nop 1.90

Hi,

Sometimes when I make a custom page like "webinar.aspx" below in my nop 1.9 sites, and then check Google Analytics I see traffic to:

http://www.mysite.com/webinar.aspx?_TSM_HiddenField_=ctl00_ctl00_cph1_cph1_ToolkitScriptManager1_HiddenField&_TSM_CombinedScripts_=%3b%3bAjaxControlToolkit%2c+Version%3d4.1.40412.0%2c+Culture%3dneutral%2c+PublicKeyToken%3d28f01b0e84b6d53e%3aen-US%3aacfc7575-cdee-46af-964f-5d85d9cdcf92%3ade1feab2%3af9cec9bc%3a8ad18101

What does that "hidden field" mean - it's certainly making for some interesting google sitemaps : )

Thanks

David