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Your web client sends its user agent to every website you connect to.
Weve written aboutchanging your browsers user agentbefore but what exactly is a user agent, anyway?
This sounds simple, but user agents have become a mess over time.
The contents of the user agent field vary from surfing app to surfing app.
Each web client has its own, distinctive user agent.
However, you might spot something confusing IE identifies itself as Mozilla.
Well come back to that in a minute.
To understand why, well have to examine the history of user agents and browsers.
The User Agent String Mess
Mosaic was one of the first browsers.
Its user agent string was NCSA_Mosaic/2.0.
Later, Mozilla came along (later renamed Netscape), and its user agent was Mozilla/1.0.
Mozilla was a more advanced internet tool than Mosaic in particular, it supported frames.
To other browsers, web servers sent the old pages without frames.
Eventually, Microsofts Internet Explorer came along and it supported frames, too.
However, IE didnt receive web pages with frames, because web servers just sent those to Mozilla browsers.
Web servers were happy to see the word Mozilla and sent IE the modern web pages.
Other browsers that came later did the same thing.
In this way, surfing app developers kept adding words to their user agents over time.
Web servers can also give orders to specific bots (or all bots) using the robots.txt file.
In the robots.txt file, the bots are identified by their user agent strings.
