The Trident/4.0 User-Agent String

In order to help users visit sites that block the “MSIE 8.0” user-agent string, IE8 will send the “MSIE 7.0” version information when viewing sites with Compatibility View enabled. As Scott described last August, a new “Trident” token in the User-Agent string allows your code to detect Internet Explorer 8 clients even when they are using the Compatibility View feature.

IE8 on Windows Vista (Compatibility View)

Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0; Trident/4.0)

IE8 on Windows Vista

Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.0; Trident/4.0)

As noted in the Best Practices for detecting the IE version, we recommend that web developers do not block access to content based on the user-agent string of the browser. If you must offer different content to different versions of the browser due to improved capabilities, you should ensure that future versions of the browser are not blocked.

Serving content based solely on the user-agent string is often an unreliable way to detect the full capabilities of the browser, because the user might have adjusted some settings, such as disabling script or extensions.

The Windows 7 User-Agent String

On Windows 7, IE8 will send the User-Agent string with the new Windows NT version token.

IE8 on Windows 7

Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.1; Trident/4.0)