For computer log management , the Common Log Format , also known as the NCSA Common log format , (after NCSA HTTPd ) is a standardized text file format used by web servers when generating server log files . Because the format is standardized, the files can be readily analyzed by a variety of web analysis programs , for example Webalizer and Analog .
31-723: Each line in a file stored in the Common Log Format has the following syntax: The format is extended by the Combined Log Format with referer and user-agent fields. A dash ( - ) in a field indicates missing data. Log files are a standard tool for computer systems developers and administrators. They record the "what happened, when, by whom" of the system. This information can record faults and help their diagnosis. It can identify security breaches and other computer misuse. It can be used for auditing. It can be used for accounting purposes. The information stored
62-423: A class-action lawsuit over the use of "undeletable" tracking cookies partially involving the use of ETags. Because ETags are cached by the browser and returned with subsequent requests for the same resource, a tracking server can simply repeat any ETag received from the browser to ensure an assigned ETag persists indefinitely (in a similar way to persistent cookies ). Additional caching headers can also enhance
93-510: A security risk. To mitigate security risks, browsers have been steadily reducing the amount of information sent in Referer. As of March 2021, by default Chrome , Chromium -based Edge , Firefox , Safari default to sending only the origin in cross-origin requests, stripping out everything but the domain name. The misspelling of referrer was introduced in the original proposal by computer scientist Phillip Hallam-Baker to incorporate
124-419: A browser, which will prevent tracking on the user's page. Do Not Track is a web browser setting that can request a web application to disable the tracking of a user. Enabling this feature will send a request to the website users are on to voluntarily disable their cross-site user tracking. Contrary to popular belief, browser privacy mode does not prevent (all) tracking attempts because it usually only blocks
155-468: A false URL, usually their own. This raises the problem of referrer spam. The technical details of both methods are fairly consistent – software applications act as a proxy server and manipulate the HTTP request, while web-based methods load websites within frames, causing the web browser to send a referrer URL of their website address. Some web browsers give their users the option to turn off referrer fields in
186-425: A website when the user visits the website. The website might then retrieve the information on the cookie on subsequent visits to the website by the user. Cookies can be used to customise the user's browsing experience and to deliver targeted ads. Some browsing activities that cookies can store are: A first-party cookie is created by the website the user is visiting. These cookies are considered "good" since they help
217-462: Is an optional HTTP header field that identifies the address of the web page (i.e., the URI or IRI ) from which the resource has been requested. By checking the referrer, the server providing the new web page can see where the request originated. In the most common situation, this means that when a user clicks a hyperlink in a web browser , causing the browser to send a request to the server holding
248-493: Is blocked by some browsers and ad blockers using block lists of known trackers. ETags can be used to track unique users, as HTTP cookies are increasingly being deleted by privacy-aware users. In July 2011, Ashkan Soltani and a team of researchers at UC Berkeley reported that a number of websites, including Hulu , were using ETags for tracking purposes. Hulu and KISSmetrics have both ceased "respawning" as of 29 July 2011, as KISSmetrics and over 20 of its clients are facing
279-504: Is hidden. Content Security Policy standard version 1.1 introduced a new referrer directive that allows more control over the browser's behaviour in regards to the referrer header. Specifically it allows the webmaster to instruct the browser not to block referrer at all, reveal it only when moving with the same origin etc. Web tracking Web tracking is the practice by which operators of websites and third parties collect, store and share information about visitors' activities on
310-673: Is only available for later analysis if it is stored in a form that can be analysed. This data can be structured in many ways for analysis. For example, storing it in a relational database would force the data into a query-able format. However, it would also make it more difficult to retrieve if the computer crashed, and logging would not be available unless the database was available. A plain text format minimises dependencies on other system processes, and assists logging at all phases of computer operation, including start-up and shut-down, where such processes might be unavailable. HTTP referer In HTTP , " Referer " (a misspelling of " Referrer " )
341-675: Is the URL of the previous web page from which a link was followed. More generally, a referrer is the URL of a previous item which led to this request. For example, the referrer for an image is generally the HTML page on which it is to be displayed. The referrer field is an optional part of the HTTP request sent by the web browser to the web server. Many websites log referrers as part of their attempt to track their users . Most web log analysis software can process this information. Because referrer information can violate privacy , some web browsers allow
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#1732780125402372-630: The EU's eCommerce Directive and the UK's Data Protection Act . When it is done without the knowledge of a user, it is considered a breach of browser security . In a business-to-business context, understanding a visitor's behavior in order to identify buying intentions is seen by many commercial organizations as an effective way to target marketing activities. Visiting companies can be approached, both online and offline, with marketing and sales propositions which are relevant to their current requirements. From
403-558: The "Referer" header field into the HTTP specification. The misspelling was set in stone by the time (May 1996) of its incorporation into the Request for Comments standards document RFC 1945 (which 'reflects common usage of the protocol referred to as "HTTP/1.0 " ' at that time); document co-author Roy Fielding remarked in March 1995 that "neither one (referer or referrer) is understood by"
434-417: The HTTP referrer sent by the web browser for each request. This raises a number of privacy concerns, and as a result, a number of systems to prevent web servers being sent the real referring URL have been developed. These systems work either by blanking the referrer field or by replacing it with inaccurate data. Generally, Internet-security suites blank the referrer data, while web-based servers replace it with
465-584: The NoScript and uBlock add-ons have assisted with developing Firefox's SmartBlock capabilities. Search Engines To safeguard user data from tracking by search engines, various privacy focused search engines have been developed as viable alternatives. Examples of such search engines include DuckDuckGo , MetaGer , and Swiscows , which prioritize preventing the storage and tracking of user activity. It's worth noting that while these alternatives offer enhanced privacy, some may not guarantee complete anonymity, and
496-590: The World Wide Web. Analysis of a user's behaviour may be used to provide content that enables the operator to infer their preferences and may be of interest to various parties, such as advertisers. Web tracking can be part of visitor management. The uses of web tracking include the following: Every device connected to the Internet is assigned a unique IP address , which is needed to enable devices to communicate with each other. With appropriate software on
527-433: The ability to give the top-level address of the target website as the referrer, which reduces these problems but can still in some cases divulge the user's last-visited web page. Many blogs publish referrer information in order to link back to people who are linking to them, and hence broaden the conversation. This has led, in turn, to the rise of referrer spam : the sending of fake referrer information in order to popularize
558-401: The destination web page, the request may include the Referer field, which indicates the last page the user was on (the one where they clicked the link). Web sites and web servers log the content of the received Referer field to identify the web page from which the user followed a link, for promotional or statistical purposes. This entails a loss of privacy for the user and may introduce
589-463: The host website, the IP address of visitors to the site can be logged and can also be used to determine the visitor's geographical location . Logging the IP address can, for example, monitor if a person voted more than once, as well as their viewing pattern. Knowing the visitor's location indicates, besides other things, the country. This may, for example, result in prices being quoted in the local currency,
620-449: The number of times a user visits. Restrictions on third-party cookies introduced by web browsers are bypassed by some tracking companies using a technique called CNAME cloaking [ de ] , where a third-party tracking service is assigned a DNS record in the first-party origin domain (usually CNAME ) so that it's masqueraded as first-party even though it's a separate entity in legal and organizational terms. This technique
651-445: The point of view of a sales organization, engaging with a potential customer when they are actively looking to buy can produce savings in otherwise wasted marketing funds. The most advanced protection tools are or include Firefox 's tracking protection and the browser add-ons uBlock Origin and Privacy Badger . Moreover, they may include the browser add-on NoScript , the use of an alternative search engine like DuckDuckGo and
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#1732780125402682-409: The preservation of ETag data. Web browsing is linked to a user's personal information. Location, interests, purchases, and more can be revealed just by what page a user visits. This allows them to draw conclusions about a user, and analyze patterns of activity. Use of web tracking is unethical when applied in the context of a private individual; and to varying degrees is subject to legislation such as
713-409: The price or the range of goods that are available, special conditions applying and in some cases requests from or responses to a certain country being blocked entirely. Internet users may circumvent censorship and geo-blocking and protect personal identity and location to stay anonymous on the internet using a VPN connection. A HTTP cookie is code and information embedded onto a user's device by
744-418: The referrer field is not sent. The HTML5 standard added support for the attribute/value rel="noreferrer" , which instructs the user agent to not send a referrer. Another referrer hiding method is to convert the original link URL to a Data URI scheme -based URL containing small HTML page with a meta refresh to the original URL. When the user is redirected from the data: page, the original referrer
775-518: The request header. Most web browsers do not send the referrer field when they are instructed to redirect using the "Refresh" field. This does not include some versions of Opera and many mobile web browsers. However, this method of redirection is discouraged by the World Wide Web Consortium (W3C). If a website is accessed from a HTTP Secure (HTTPS) connection and a link points to anywhere except another secure location, then
806-468: The spammer's website. It is possible to access the referrer information on the client side using document.referrer in JavaScript . This can be used, for example, to individualize a web page based on a user's search engine query. However, the referrer field does not always include search keywords, such as when using Google Search with HTTPS. Most web servers maintain logs of all traffic, and record
837-545: The standard Unix spell checker of the period. "Referer" has since become a widely used spelling in the industry when discussing HTTP referrers; usage of the misspelling is not universal, though, as the correct spelling "referrer" is used in some web specifications such as the Referrer-Policy HTTP header or the Document Object Model . When visiting a web page, the referrer or referring page
868-430: The storage of information on the visitor site ( cookies ). It does not help, however, against the various fingerprinting methods. Such fingerprints can be de-anonymized . Many times, the functionality of the website fails. For example, one may not be able to log in to the site, or preferences are lost. Some web browsers use "tracking protection" or "tracking prevention" features to block web trackers. The teams behind
899-599: The use of a VPN . However, VPNs cost money and as of 2023 NoScript may "make general web browsing a pain". On mobile, the most advanced method may be the use of the mobile browser Firefox Focus , which mitigates web tracking on mobile to a large extent, including Total Cookie Protection and similar to the private mode in the conventional Firefox browser. Users can also control third-party web tracking to some extent by other means. Opt-out cookies let users block websites from installing future cookies. Websites may be blocked from installing third-party advertisers or cookies on
930-456: The user rather than spy on them. The main goal of first-party cookies is to recognize the user and their preferences so that their desired settings can be applied. A third-party cookie is created by websites other than the one a user visits. They insert additional tracking code that can record a user's online activity. On-site analytics refers to data collection on the current site. It is used to measure many aspects of user interactions, including
961-452: The user to disable the sending of referrer information. Some proxy and firewall software will also filter out referrer information, to avoid leaking the location of non-public websites. This can, in turn, cause problems: some web servers block parts of their website to web browsers that do not send the right referrer information, in an attempt to prevent deep linking or unauthorised use of images ( bandwidth theft ). Some proxy software has