We have a .NET app that we’ve deployed to some systems. We also have a URL that we assume is only published via our .NET app and not known on any other page. We are tracking user agents with MSIE in them and sending them to a file. When we check the file, yes, the predominent number of them have .NET in the user agent string. But a few of them do not. For instance:
Mozilla/5.0 (compatible; MSIE 9.0; Windows NT 6.1; Trident/5.0; BOIE9;ESMX)
Mozilla/5.0 (compatible; MSIE 9.0; Windows NT 6.0; Trident/5.0)
Mozilla/5.0 (compatible; MSIE 9.0; Windows NT 6.1; WOW64; Trident/5.0)
I guess we can make only two conclusions from this. One would be that our assumption that the registration page is accessible from some other link on the web (like Google found it). Another would be that someone has changed their user agent string with some tool/plugin/extension. Still another would be that some IE versions, even with .NET installed, do not announce their .NET in the user agent.
Our question to you is — is there a case where .NET is installed, and MSIE is in the user agent, and it doesn’t send us the .NET versions, if we assume that someone hasn’t altered their user agent string with a fake string?
Microsoft states in the link below that as of IE9, they stopped putting feature tokens for .NET in the user agent because they said it was breaking functionality on some web servers.
http://msdn.microsoft.com/en-us/library/ms537503(v=vs.85).aspx
…but as one other user mentioned above, proxies and antivirus software can sometimes alter the user agent string too, and so can some plugins/addons/extensions.