IE10 and IE11 user agent strings

Web developers, especially those playing the browser detection game, are on a different kind of treat with IE11. Starting with IE11 (part of Windows 8.1), the regular user agent string will change, and will not anymore contain the string "MSIE" that has been used for ages to detect Internet Explorer.

Here's how IE10 reports itself on Windows 7, 32-bit:

User-Agent: Mozilla/5.0 (compatible; MSIE 10.0; Windows NT 6.1; Trident/6.0)

And here's how the latest IE11 on Windows 8.1 "Blue" preview reports itself:

User-Agent: Mozilla/5.0 (Windows NT 6.3; WOW64; Trident/7.0; rv:11.0) like Gecko

Note how there is no "MSIE" marker anymore, and the words "like Gecko" have been added. Curiously, the version (or rather, the revision or "rv") is still present, but using the rv marker.

Since many websites and applications rely on detecting IE and treating it different from other browsers, by taking out this key detection string, many web sites will start working like you were using, say, Firefox or Chrome. Of course, you can still detect the Trident view engine as IE, but this isn't what many sites do.

For more information about compatibility with IE11, check out this preliminary document on MSDN.