# History of Instant Messaging:
In the early 1990s, people began to spend more and more time on the Internet. Creative software developers designed chat-room software and set up chat rooms on Web servers. In a chat room, a group of people can type in messages that are seen by everyone in the "room." Instant messages are basically a chat room for just two people. Instant messaging really exploded on the Internet scene in November 1996. computer.howstuffworks.com 
In 1997, AOL, considered the pioneer of the online community, gave its users the ability to talk in real time with each other through chat rooms and instant messages. The ICQ model is the basis for most instant-messaging utilities on the market today. In the next section we'll examine how these services work.
#. How does Instant Messaging work?
Instant messaging works as its name. It delivers the user’s message to his desired contact instantly. The message delivery is instant provided users contact person is online. The client software allows user to maintain a list of contacts that he wants to communicate. User can send messages to any of the contacts in his list. Such list is referred to as a buddy list or contact list. The contact list can be managed by adding, deleting or editing the contacts e-mail ID and other related information. Also a group can be formed of different ID. User can also block a particular contact or everyone who is not on his contact list from sending an instant message. Setting the appropriate privacy settings does this. sans.org 
Sometimes user is online but is busy and do not wish to respond to any instant messages. In such situations user can change his status to ‘Busy’ or ‘Not available’. This allows the person who is trying to contact user know the reasoning behind the non-availability of user. User can also choose to be invisible while being online. This enables him to watch his contacts without giving his status. Also, User can have an individual chat session or have a conference with multiple users. With use of web camera and voice an interactive web conference can be held using instant messaging.
#. Instant Messaging Service Providers:
Among the various vendors for instant messaging, America online (AOL), Yahoo and Microsoft are some of the major vendors in providing instant messaging for consumers, with AOL in the lead.
AOL Instant Messenger (AIM). AOL has 35 million members worldwide. AIM delivers over 1.38 billion instant messages daily across the AOL network. AOL is considered to have most of the IM Market share due to its vast online user base. AIM client is provided via download, to any of its customers. sans.org 
MSN Messenger has about 9 million subscriptions. Besides the subscribers, MSN Messenger can be downloaded free of charge by anyone with an access to Internet.
Yahoo Instant Messenger, Yahoo provides the Messenger services free of charge to anyone who wants it. Both Yahoo and MSN support instant text and voice messages, communication face-to-face via web cameras, and affordable PC-to-phone calls anywhere in the world. Users have sent approximately 17 billion messages in December 2002 alone. In 2002, Yahoo took the IM sensation mobile through an agreement with AT&T Wireless. sans.org 
#. DESIGN GOALS
The main feature of the protocol is to prevent an adversary to read / intercept the instant messages so as to retain the privacy between