User Agent String.Com 

User Agent String explained :

Mozilla 1.0.1
Mozilla	Name : Mozilla
5.0	Mozilla version
X11	X Window System a windowing system for bitmap displays
U	Security values: N for no security U for strong security I for weak security
Linux i686	Operating System: Linux running on a Intel Pentium Pro CPU
en-US	Language Tag, indicates the language for which the client had been localized (e.g. menus and buttons in the user interface) en-US = English - United States
rv:1.0.1	CVS Branch Tag The version of Gecko being used in the browser For the Mozilla browser this is the browser version as well
Gecko	Gecko engine inside
20020903	Build Date: the date the browser was built
All Mozilla user agent strings