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There are sites like whatsmybrowser.org and whatismybrowser.com that detect information about the technical specs of the client. As far as I can tell, this is done using the user-agent information sent by the browser on the HTTP requests.

What is puzzling me is that when I explicitly set my user-agent string to something random, in some cases it can still detect my browser and OS.

For example, whatbrowser.org knows I am using Firefox 31; and www.whatsmyua.com displays the following string:

Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:31.0) Gecko/20100101 Firefox/31.0

It looks strikingly like a user-agent.

enter image description here

But where is it being detected from? Firebug shows just fake-user-agent sent on the HTTP request headers.

If it matters, I am faking my user-agent using UAControl for Firefox (pt-br version, en-US version).

Scott - Слава Україні
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That Brazilian Guy
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1 Answers1

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I am not sure what those sites in particular are doing, but it is possible to probe a browser with JavaScript to detect its capabilities and identification. That is how progressive enhancement is done.

That Brazilian Guy
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Todd
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