Why is my HTTP_USER_AGENT not always the same?

Question

When I print my ENV {'HTTP_USER_AGENT'} at the beginning of my perl page, sometimes it says that I use IE7, and sometimes I say that I use IE8. Any idea why?

Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 5.1; Trident/4.0; .NET CLR 1.1.4322; 
InfoPath.1; .NET CLR 2.0.50727; .NET CLR 3.0.04506.30; .NET CLR 3.0.04506.648; 
.NET CLR 3.0.4506.2152; .NET CLR 3.5.30729)

Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.1; Trident/4.0; .NET CLR 1.1.4322;
InfoPath.1; .NET CLR 2.0.50727; .NET CLR 3.0.04506.30; .NET CLR 3.0.04506.648;
.NET CLR 3.0.4506.2152; .NET CLR 3.5.30729)

My version of IE is actually 8.

Answer 1

IE 8 will claim IE 7 for backward compatibility reasons - this is called the compatibility view.

Additional information: http://msdn.microsoft.com/en-us/library/dd567845%28VS.85%29.aspx

(, , IE 7) -. ,

res://iecompat.dll/iecompatdata.xml

IE.

Answer 2

IE8 IE7, , IE7. , IE8 -, IE7 Internet Explorer.

IE8 IE7

Answer 3

Are you using IE8 compatibility mode that makes your browser behave like IE7 and present itself as such?