User agents refer to applications that access the internet such as web browsers, mobile phones and portable devices implementing communication sessions.
The USER-AGENT string
The application accessing a web site or service identifies itself via a user-agent string which provides information such as application type, operating system, installed software and versions.
Web servers that receive connection requests read these user-agent strings in order to determine the type of device that is making a connection so that they can determine how to handle the reply, such as serving a mobile version of a web site to a mobile phone rather than the full site that a PC's web browser would receive.
Web servers can also use user-agent strings to block specific types of device or any other variable that appears in the user-agent string such as computers without a specific application installed.
Spoofing user agents
It is possible to fake or spoof your user agent string so that the remote site thinks that you are a different type of device or application so that you are not blocked and or can gain access to a specific version of the data being served by the remote site.
Spoofing your user-agent string is also a good way of remaining anonymous and reducing the ability of remote sites to track you.
User-agent strings identify your device, its operating system and installed software to the receiving computer. The receiving computer can read this information and decide what to send back. The information you provide in your user-agent string can be spoofed (faked) to hide your real system details from the receiving computer.
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Article date: 27th February 2011