Sunday, August 15, 2010

What is an internet cookie ?

An internet cookie is a small piece of text or data sent by a remote web server (server computer) and stored in a file on your computer by the browser that you are using while surfing the web. A cookie is also called as a web cookie, browser cookie, or HTTP cookie. A cookie is used for authentication of a website, storing site preferences, shopping cart contents, identifier for a session on a computer, personalization, user behavior etc. A web server will request a cookie later and the browser retrieves it from where it is stored in the computer. Cookie consists of name-value pairs containing bits of information which is encrypted for privacy and security reasons. The information contained in the cookie can actually be used to track your identity, preferences, and your actions while you navigate the web. Cookies has an expiration date associated with them and will be deleted automatically when the expiration date has passed. These are not executable files as it is a text file and will not replicate themselves like viruses.

Because the browsers can read and set a cookie, they can be used as a spyware to track user behavior. Some cookies can infringe on the privacy of the users and can be possible malware, which is identified by a good anti-spyware/anti-malware program. Cookies can be cleared manually like how we clear the internet cache or browsing history. There are browser settings whether to accept cookies and the time frame to keep any of them. Rejecting cookies altogether may make some websites unusable because cookies are needed by some websites for authentication and secure transaction like mail websites, online payment websites etc. So it is advisable that you do clear all cookies before logging into these websites.

Many websites use cookies for personalization based on user's preferences. Users select their preferences by entering them in a web form and submitting the form to the server. The server encodes the preferences in a cookie and sends the cookie back to the browser. Every time the user accesses a web page, the server is also sent the cookie where the preferences are stored, and can personalize the page according to the user preferences. It is then possible to find out which pages the user has visited and in what sequence. The log contains the requests done using a specific cookie ID and it can be determined whether the requests have come from the same user. The URL and date/time stored with the cookie allows for finding out which pages the user has visited, and at what time.

Server and browser use the cookie transaction introducing a state or memory of previous events of HTTP transactions. Without cookies each retrieval of a web page or component of a web page is an isolated event, unrelated to all other views of the pages of the same site. Tracking within a website is typically used to produce usage statistics, while tracking across websites is typically used by advertising companies to produce anonymous user profiles. A tracking cookie may infringe upon the user's privacy while surfing anonymous websites but they can be easily removed.

You can manually delete any cookies by clearing it from the browser thus permanently deleting it from the computer.
To delete cookies in Internet Explorer:
Go to Tools menu > choose Internet Options > in the General tab > at the temporary internet files column click Delete Cookies > a dialog box asks for confirmation > click Ok.
To delete cookies in Mozilla Firefox:
Go to Tools menu > choose Clear Recent History > check cookies from the check box > then click Clear Now button.
To delete cookies in Google Chrome:
Go to customize and control menu > select Options > choose Under the Hood tab > click Clear Browsing Data button > check Delete cookies and other site data check box.

Current versions of popular web browsers include options to delete 'persistent' cookies when the application is closed.
You can also make browser setting to delete cookies automatically when closing the browser.
To delete cookies automatically in Mozilla Firefox:
Go to Tools menu > choose Options > check clear history when Firefox closes check box > click Ok.

Monday, August 2, 2010

What is a URL and what are the different components of it

A URL is actually a link, which connects you to a website. It is also called as a Uniform Resource Locator. This is a unique address for a file that is accessible on the Internet. eg.  A common way to get to a web site is to enter the URL of its home page file in your Web browser's address line. The target website is contacted using a hypertext transfer protocol, which identifies the website and transfer the contents to the end user. The Uniform Resource Locator was created in 1994 by Tim Berners-Lee, Marc Andreessen, Mark P. McCahill, Alan Emtage, Peter J. Deutsch and Jon Postel, as part of the URI. The URL consists of various components to describe the full length of it.

Every URL consists of the 1) the scheme name or  protocol followed by a colon, then depending on scheme, 2) a hostname (server name or alternatively an IP address), 3) a port number, the path of the resource to be fetched or the program to be run, then, for programs such as Common Gateway Interface (CGI) scripts, 4) a query string and with HTML documents an anchor (optional) for where the page should start to be displayed.

      The basic components in a URL are:

      http:        //       /products/          laptop.html

   protocol          server name           directory name      page or file name

1) Protocol comes first and ends with a colon eg. http:
2) Server name comes then, prefixed with a double slash eg. //

    Server name further divided into:
a) Server's name eg. www
b) Domain name eg.
3) Directory which comes next with slashes before and after eg. /products/
4) Actual Page / file name comes last eg. laptop.html

A URL for a particular image on a web site will look like this:
A URL for a file meant to be downloaded using the File Transfer Protocol (FTP) would require that the "ftp" protocol be specified like this:
A URL to email a message to someone would be like this:




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