Ad-blockers are essentially a plug-in for your browser that try to prevent all those [pesky] ads from showing on your browser. They can also be located in several other places along your browsing data stream.

How do ad-blockers work?

In a nutshell, ad-blockers use a list of computer names that are known to serve ads on the internet and redirects any call to them to what is essentially a black-hole from where no data is returned. The result is that you get shown no ads while you are browsing the net.

Your computer has to do a name resolution to find the address, a long string of zeros and ones, by which to call up the server computer. For us humans it is virtually impossible to remember strings of 32 zeros and ones (IPv4) much less strings of 128 zeros and ones (IPv6) that computer use to identify each computer on the network. Meanwhile computers can not handle human-readable names such as “bigcloset.us” efficiently.

So back in the beginning of the Internet each connected computer had a “hosts” file that listed the name and corresponding address of every known computer on the network. This file still exists on every computer that uses the IP network protocol. Though it usually only has one or two entries for the so-called localhost or loopback.

As the Internet started to grow, maintaining the “hosts” file on each and every connected computer became a nightmare. That was when the “Domain Name System” or DNS was developed. It is a distributed database of computer names and addresses that allows the administrator of each small network to manage and maintain “hosts” list of their own computers. And it gets automatically shared with the rest of the Internet.

So when trying to find the address for a specific computer the “Name Resolution System” will first check in the “hosts” file. If it finds the address there, that is the end of the search. Otherwise it will ask the local DNS server. As a response it will either get the address of the computer name, or it will get the address of another DNS server. This will repeat until it finds or resolves the address of the named computer.

Ad-blockers use to DNS name resolution standard to virtually add the known ad-server names to the local “hosts” file and link them to the loopback address. And since by convention the loopback address only responds to “are you alive?” ping request, it is a virtual black hole as far as any other internet service is concerned.

Why are ever more “free” sites complaining to users about the [supposed] use of ad-blockers?

Well running a website costs money! (What a surprise!!) So many sites sell ad space in order to be able to provide “free” information or services. It is similar to open TV or radio where often half the time of a program is spent on commercial breaks.

Websites get a fraction of a penny for each ad that is called from that site. The more times a page gets visited, the more times those ads get called, and those penny fractions do add up. Consequently when no ads get called from a website, that website can not collect that revenue.

There are so many active technologies involved in web-serving that even so called read-only web pages have some form of two-way communication with the reader/client.

As somebody asserted in another forum: When a website offers a free product, the real product is the user. So like it or not, ads served on websites keep a lot of information available and affordable to the vast majority of Internet users. But at the same time they collect a lot of information and data about those self-same users. And that data and information is then used to entice those self-same users to spend their hard-earned money (or money they do not really have) on products and/or services they do not really need or can not really afford.

In the end it all boils down to money, and how much of it corporations can press out of Jane Doe.