ADSL is known as an “always-on” technology. This means that users do not have to make a phone call to connect to the Internet. The ADSL line is always connected to the local telephone exchange and is always available. However, the telephone company (Telkom) and/or the Internet Service Provider (IS), may logically disconnect any session after a defined time of inactivity has passed, forcing users to login periodically. Unlike dial-up connections, however, users do not pay based on the amount of time that they are connected - the monthly line rental provides for continuous availability of access.

In information technology, the term domain can refer to:

a machine or virtual host on the Internet; the name of a domain (the "domain name") can be confused with the domain itself.
a Windows Server domain, a centrally-managed group of computers using the Windows operating-system
a broadcast domain in computer networking
an application domain - the kinds of purposes for which users use a software system
a software engineering domain - a field of study that defines a set of common requirements, terminology, and functionality for any software program constructed to solve a problem in that field. See also domain-specific programming languages.
a CLR application domain, a mechanism for separating executed applications (similar to a process)
In Database Theory, a data domain is a set of all permitted atomic values.
a workstation operating system called Domain/OS.
a group of computers on a network that share a common directory or storage locations.

The term domain name has multiple related meanings:

A name that identifies a computer or computers on the internet. These names appear as a component of a Web site's URL, e.g. wikipedia.org. This type of domain name is also called a hostname.
The product that domain name registrars provide to their customers. These names are often called registered domain names.
Names used for other purposes in the Domain Name System (DNS), for example the special name which follows the @ sign in an email address, or the Top-level domains like .com, or the names used by the Session Initiation Protocol (VoIP), or DomainKeys.
They are sometimes colloquially (and incorrectly) referred to by marketers as "web addresses".

This article will primarily discuss registered domain names. See the Domain Name System article for technical discussions about general domain names and the hostname article for further information about the most common type of domain name.

The most common types of domain names are hostnames that provide more memorable names to stand in for numeric IP addresses. They allow for any service to move to a different location in the topology of the Internet (or an intranet), which would then have a different IP address.

By allowing the use of unique alphabetical addresses instead of numeric ones, domain names allow Internet users to more easily find and communicate with web sites and other server-based services. The flexibility of the domain name system allows multiple IP addresses to be assigned to a single domain name, or multiple domain names to be assigned to a single IP address. This means that one server may have multiple roles (such as hosting multiple independent Web sites), or that one role can be spread among many servers. One IP address can also be assigned to several servers, as used in anycast and hijacked IP space.

Hostnames are restricted to the ASCII letters "a" through "z" (case-insensitive), the digits "0" through "9", and the hyphen, with some other restrictions. Registrars restrict the domains to valid hostnames, since, otherwise, they would be useless. The Internationalized domain name (IDN) system has been developed to bypass the restrictions on character allowances in hostnames, making it easier for users of non-english alphabets to use the Internet. The underscore character is frequently used to ensure that a domain name is not recognized as a hostname, for example with the use of SRV records, although some older systems, such as NetBIOS did allow it. Due to confusion and other reasons, domain names with underscores in them are sometimes used where hostnames are required.

The following example illustrates the difference between a URL (Uniform Resource Locator) and a domain name:

URL: http://www.example.net/index.html
Domain name: www.example.net
Registered domain name: example.net
As a general rule, the IP address and the server name are interchangeable. For most Internet services, the server will not have any way to know which was used. However, the explosion of interest in the Web means that there are far more Web sites than servers. To accommodate this, the hypertext transfer protocol (HTTP) specifies that the client tells the server which name is being used. This way, one server with one IP address can provide different sites for different domain names. This feature goes under the name virtual hosting and is commonly used by Web hosts.

For example, as referenced in RFC 2606 (Reserved Top Level DNS Names), the server at IP address 192.0.34.166 handles all of the following sites:

example.com
www.example.com
example.net
www.example.net
example.org
www.example.org
When a request is made, the data corresponding to the hostname requested is served to the user.

Spam is one of the most significant threats to the Internet, accounting for around 60% of all email traffic. Spam costs consumers and ISPs lots of money in bandwidth charges. Despite the growing number of technological means for combating spam, the spammers somehow manage to stay one step ahead and the deluge shows little sign of abating.

Spammers get email addresses in a variety of manners:

* They can write program which searches the web in spider-like fashion, following links to pages, and the links of those pages to other pages, to infinity. As part of this link following process the program will search for obvious email addresses such as email@address.com or HTML mailto: links. In a short space of time many thousands of email addresses can be harvested in this fashion.
* They can purchase an existing email address database from someone who runs a continuous spider program. Often selling for a few dollars and amounting to millions of email addresses, the purchase of such databases occurs not just by spammers but also more legitimate firms seeking new manners of advertising their product or service in a state of ignorance over spam.
* They can brute force an SMTP server, trying various common names for people and well known role accounts.
* Someone might willingly or unwittingly add your address to an opt-in mailing list for adverts.

One of the ways in which spammers check for valid addresses is by providing an apparently thoughtful Click here to remove yourself from this list with a URL pointing to a website. The user seeking to prevent further mails from the spammer clicks the link in a trusting fashion. However all they have done is verify that their email address is active, which results in additional spam being sent to them.

Another means is to insert a pixel image into the email which links to a web server. When you load the message in an HTML capable mail client, the mail client requests the pixel image from the configured web server. By accessing the image and downloading it, a line is added to the web server log file which can be used to verify an address which spam was sent to.

Why is spam bad?

Spam is bad because users are forced to pay to download content they didnt ask to receive. In many cases users find themselves downloading more spam than legitimate email messages and this dilutes the value of Internet based communication. No-one wants to wade through spam to find the legitimate content.

While ISPs have to bear the bulk of the cost for bandwidth overuse by spammers, this cost is often passed onto the consumer through increased Internet access fees or a degraded service level.

Users themselves are at their wits end, as the process of manually deleting spam is burdensome. Some email clients have special filters which allow for the recognition of spam based on existing messages marked as spam. In addition a number of software companies sell anti-spam software in addition to anti-virus software or content filtering systems.

Spammers generally do not pay much for the sending of spam. They exploit open mail servers to do their task for them. The spammer need only send one email message to an incorrectly configured mail server to reach thousands of email addresses, with the bulk of the transfer being handled by the mis-configured mail server. Recipients in turn need to pay access costs or telephone costs in order to receive content they didnt ask for.

More information can be found here: http://spam.abuse.net/overview/