A user agent is the client application used with a particular network protocol; the phrase is most commonly used in reference to those which access the World Wide Web, but other systems such as SIP uses the term user agent to refer to the user's phone. A client is an application or system that accesses a remote service on another Computer system, known as a server, by way of a Network. In computing, a protocol is a convention or standard that controls or enables the connection Communication, and Data transfer between two computing The World Wide Web (commonly shortened to the Web) is a system of interlinked Hypertext documents accessed via the Internet. The Session Initiation Protocol ( SIP) is a signalling protocol widely used for setting up and tearing down Multimedia Communication sessions Web user agents range from web browsers and e-mail clients to search engine crawlers ("spiders"), as well as mobile phones, screen readers and braille browsers used by people with disabilities. A web browser is a software application which enables a user to display and interact with text images videos music games and other information typically located on a An e-mail client, aka Mail User Agent (MUA aka e-mail reader is a frontend Computer program used to manage E-mail. A web crawler (also known as a web spider, web robot, or—especially in the FOAF community— web scutter) is a program or automated A screen reader is a software application that attempts to identify and interpret what is being displayed on the screen (or more accurately sent to standard output The Braille system is a method that is widely used by blind people to read and write When Internet users visit a web site, a text string is generally sent to identify the user agent to the server. In Computer programming and some branches of Mathematics, a string is an ordered Sequence of Symbols. The term web server can mean one of two things A Computer program that is responsible for accepting HTTP requests from web clients which are This forms part of the HTTP request, prefixed with User-Agent: (case does not matter) and typically includes information such as the application name, version, host operating system, and language. Hypertext Transfer Protocol ( HTTP) is a Communications protocol for the transfer of information on the Internet. An operating system (commonly abbreviated OS and O/S) is the software component of a Computer system that is responsible for the management and coordination Bots, such as web crawlers, often also include a URL and/or e-mail address so that the webmaster can contact the operator of the bot. Internet bots, also known as web robots, WWW robots or simply bots, are software applications that run automated tasks over the Internet Uniform Resource Locator is an URI which also specifies where the identified resource is available and the protocol for retrieving it An e-mail address identifies a location to which E-mail messages can be delivered The webmaster (feminine webmistress) also called the Web architect, the Web developer, the site author, or the website
The user-agent string is one of the criteria by which crawlers can be excluded from certain pages or parts of a website using the "Robots Exclusion Standard" (robots. The robot exclusion standard, also known as the Robots Exclusion Protocol or robots txt). This allows webmasters who feel that certain parts of their website should not be included in the data gathered by a particular crawler, or that a particular crawler is using up too much bandwidth, to request that crawler not to visit those pages.
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User agent spoofing
At various points in its history, use of the Web has been dominated by one browser to the extent that many websites are designed to work with that particular browser, rather than according to standards from bodies such as the W3C and IETF. Such sites often include "browser sniffing" code, which alters the information sent out depending on the User-Agent string received. This can mean that less popular browsers are not sent complex content, even though they might be able to deal with it correctly, or in extreme cases refused all content. Thus various browsers "cloak" or "spoof" this string, in order to identify themselves as something else to such detection code; often, the browser's real identity is then included later in the string.
The earliest example of this is Internet Explorer's use of a User-Agent string beginning "Mozilla/<version> (compatible; MSIE <version>. Windows Internet Explorer (formerly Microsoft Internet Explorer abbreviated MSIE) commonly abbreviated to IE, is a series of graphical . . ", in order to receive content intended for Netscape Navigator, its main rival at the time of its development. Netscape Navigator and Netscape are the names for the proprietary Web browser popular in the 1990s and the Flagship product of the Netscape This was not a reference to the open-source Mozilla browser, which was developed much later, but to the original codename for Navigator, which was also the name of the Netscape company mascot. Mozilla was the official public original name of Mozilla Application Suite by the Mozilla Foundation, currently known as SeaMonkey suite. Mozilla was the Mascot of the now disbanded Netscape Communications Corporation. This format of User-Agent string has since been copied by other user agents, partly because Explorer, in turn, came to dominate.
When Internet Explorer became the dominant web browser, rivals such as Firefox, Safari, and Opera implemented systems whereby the user could select a false User-Agent string to send, such as that of a recent version of Explorer. Safari is a Web browser developed by Apple Inc and included in Mac OS X. Opera is a Web browser and Internet suite developed by the Opera Software company Some – e. g. Firefox and Safari – duplicate the User-Agent string they are trying to spoof exactly; others – e. g. Opera – duplicate the User-Agent string but add the genuine browser name to the end. This latter approach, of course, leads to a string containing three names and versions: first, the user agent claims to be "Mozilla" (i. e. Netscape Navigator); then, "MSIE" (Internet Explorer); and finally, the actual browser, such as "Opera". Opera also offers a full masking as Internet Explorer or Firefox, which hides "Opera" completely.
Beside browsers, other programs utilizing HTTP protocol, like most download managers and offline browsers, also had the ability to change the user agent string sent to servers to user's liking. A download manager is a Computer program dedicated to the task of downloading (and sometimes uploading) possibly unrelated stand-alone files from (and This is presumably done in an effort to maintain compatibility with certain servers (some servers refused to serve those programs right away because they are mostly used carelessly, thus burdening the server).
This vicious circle is expected to continue in the arena of web browsers. A virtuous circle or a vicious circle is a complex of events that reinforces itself through a Feedback loop toward greater instability Some standards-based web developers have started the "Viewable With Any Browser" campaign which encourages developers to design webpages according to official standards, not for any particular browser(s).
One result of user agent spoofing is that the usage share of Internet Explorer, the user agent browsers typically spoof, is probably overestimated, and the usage share of other browsers may be underestimated. Usage share, in Web browser statistics is the percentage of visitors to a group of web sites that use a particular browser User agent spoofing can also provide a security issue by spoofing search engine bots and bypassing key parts in a website.
User agent sniffing
The term user agent sniffing refers to websites that show different content when viewed with a certain user agent. On the Internet, this will result in a different site being shown when browsing the page with a specific browser (e. g. Microsoft Internet Explorer). An infamous example of this is Microsoft's Outlook 2003 Web Access. Microsoft Corporation is an American multinational Computer technology Corporation, which rose to dominate the Home computer Microsoft Outlook or Outlook (full name Microsoft Office Outlook since Outlook 2003 is a Personal information manager from Microsoft, and is When viewed with IE, much more functionality is displayed compared to the same page in any other browser. User agent sniffing is mostly considered poor practice for Web 2.0 web sites, since it encourages browser specific design. Web 20 is a term describing changing trends in the use of World Wide Web technology and Web design that aims to enhance Creativity, secure Many webmasters are recommended to create an HTML markup that is as standardised as possible, to allow correct rendering in as many browsers as possible.
Websites specifically targeted towards mobile phones, like NTT DoCoMo's I-Mode or Vodafone's Vodafone Live! portals, often rely heavily on user agent sniffing, since browsers on mobile phones often differ a lot from each other. is the predominant Mobile phone operator in Japan The name is officially an abbreviation of the phrase " do co mmunications over the mo bile network NTT DoCoMo 's i-mode is a Wireless internet service popular in Japan. Vodafone is a Mobile network operator headquartered in Berkshire, England, UK. Vodafone live! is the brand name for the multimedia portal service of Mobile phone operator Vodafone, which was initially developed by Japan's J-Phone under Many developments in mobile browsing have been made in the last few years, while many older phones that do not possess these new technologies are still heavily used. Therefore, mobile webportals will often generate completely different markup code depending on the mobile phone used to browse them. These differences can be small (e. g. resizing of certain images to fit smaller screens), or quite extensive (e. g. rendering of the page in WML instead of XHTML). Wireless Markup Language, based on XML, is a Markup language intended for devices that implement the Wireless Application Protocol (WAP specification The Extensible Hypertext Markup Language, or XHTML, is a
There are a number of ways to perform user agent sniffing within web applications, including using public domain scripts and even commercial products such as BrowserObject or BrowserHawk. See the External Links section for details.
Encryption strength "U" / "I" / "N"
Browsers created in the United States, such as Netscape Navigator, Internet Explorer, and some others, use one of these three letters to specify the browser's encryption strength. Netscape Navigator and Netscape are the names for the proprietary Web browser popular in the 1990s and the Flagship product of the Netscape Windows Internet Explorer (formerly Microsoft Internet Explorer abbreviated MSIE) commonly abbreviated to IE, is a series of graphical Since the US government formerly would not allow encryption higher than 40-bit to be exported from their country, different versions were released with different encryption strengths. "U" stands for "USA" (for the version with 128-bit encryption), "I" stands for "International" (the browser has 40-bit encryption and can be used anywhere in the world), "N" stands for "None" (no encryption). Originally the "U" version of such browsers was only available for download to those in the USA, and to get 128-bit encryption, a non-American browser like Opera had to be used. Opera is a Web browser and Internet suite developed by the Opera Software company The US government has since loosened its policy and exporting high encryption is now permitted to most countries (see Export of cryptography for more information). The export of cryptography is the transfer from one country to another of devices and technology related to Cryptography. Now Netscape and Mozilla distribute their browsers only in a "U" version, supporting up to 256-bit encryption, since an international version is no longer required. Netscape Communications (formerly known as Netscape Communications Corporation and commonly known as Netscape) is an American computer services company The Mozilla Foundation is a Non-profit organization that exists to support and provide leadership for the Open source Mozilla project
This information can be seen in Mozilla Firefox browser: Type about:config and search string general. useragent. security.
See also
External links
- User-agents.org, database of known user agent strings
- User agent string analysis
- A database of web browsers and the JavaScript properties which they support
Dictionary
user agent
-noun
- (computing) The client application used with a particular network protocol, such as http: or ftp:.
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