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Ad blocking or ad filtering is a type of software (or less commonly, a computer hardware device), that can remove or alter advertising content from a webpage, website, or a mobile app. Ad blockers are available for a range of computer platforms, including desktop and laptop computers, tablet computers and smartphones. A variety of methods have been used to block advertisements. The benefits of this software are wide-ranging and the use of ad blocking software is increasing. Some websites have taken counter-measures against users who block advertisements.
- 1 Technologies and native countermeasures
- 2 Rationales for blocking
- 3 Benefits
- 4 Popularity
- 5 Alternatives
- 6 Methods
- 7 Economic consequences for online business
- 8 Advertiser countermeasures and justifications
- 9 Advertiser network blocking
- 10 See also
- 11 References
Technologies and native countermeasures
Online advertising exists in a variety of forms, including web banners, pictures, animations, embedded audio and video, text, or pop-up windows, and can employ audio and video autoplay. All browsers offer some ways to remove or alter advertisements: either by targeting technologies that are used to deliver ads (such as embedded content delivered through browser plug-ins or via HTML5), targeting URLs that are the source of ads, or targeting behaviours characteristic to ads (such as the use of HTML5 autoplay of both audio and video).
Rationales for blocking
Computer device users employ ad blocking software and devices for a range of reasons. Ad blockers can reduce or eliminate the number of unwanted, unsolicited pop up ads which appear on the user's display. These pop-up ads can make it hard for users to see the content they intend to view, and the user may have to take an action (e.g., minimizing or closing the ad) to continue their use of the Internet. Another reason that users employ ad blockers is because unwanted ads can take up a lot of a computer's processing power, thus slowing down its performance. As well, Internet advertising can contain computer viruses, malware or fraudulent messages ("phishing") that are designed to deceptively obtain a user's password, credit card number or other private information.  In the mobile field, where people pay for actual bandwidth used, media-rich ads, such as digital videos that often auto-play, consume the amount of data allotted for the users' mobile data plan — effectively stealing the megabytes and money that people have paid to use for their own purposes.
Advertisers, on the other hand, argue that Internet ads provide revenue to website owners, which enable the website owners to create or otherwise purchase content for the website. Advertisers claim that the prevalent use of ad blocking software and devices could adversely affect website owner revenue and thus in turn lower the availability of free content on websites.
To users, the benefits of ad blocking software include quicker loading and cleaner looking web pages with fewer distractions,  lower resource waste (bandwidth, CPU, memory, etc.), and privacy benefits gained through the exclusion of the tracking and profiling systems of ad delivery platforms. Blocking ads can also save substantial amounts of electrical energy and lower users' power bills.
Ad blocking software may have other benefits to users' quality of life, as it decreases Internet users' exposure to advertising and marketing industries, which promote the purchase of numerous consumer products and services that are potentially harmful or unhealthy and on creating the urge to buy immediately.  With the average person seeing more than 5000 advertisements every day, and with many of these being from online sources, and with each ad promising viewers that their lives will be improved if they buy what is being promoted (e.g., fast food, soda pop, candy, expensive consumer electronics) or encourage users to get into debt or gamble. As well, if Internet users buy all of these items, the packaging and the containers (in the case of candy and soda pop) end up being disposed of, leading to environmental impacts of waste disposal. Advertisements are very carefully crafted to target weaknesses in human psychology; as such, a reduction in exposure to advertisements could be beneficial for users' quality of life.
Unwanted advertising can also harm the advertisers themselves, if users become annoyed by the ads. Irritated users might make a conscious effort to avoid the goods and services of firms which are using annoying "pop-up" ads which block the Internet content the user is trying to view. For users not interested in making purchases, the blocking of ads can also save time. Any ad that appears on a website exerts a toll on the user's "attention budget", since each ad enters the user's field of view and must either be consciously ignored or closed, or dealt with in some other way. A user who is strongly focused on reading solely the content that he/she is seeking, likely has no desire to be diverted by advertisements that seek to sell unneeded or unwanted goods and services. In contrast, users who are actively seeking items to purchase, might appreciate advertising, in particular targeted ads.
Ad blocking can also save money for the user. If a user's personal time is worth one dollar per minute, and if unsolicited advertising adds an extra minute to the time that the user requires for reading the webpage (i.e. the user must manually identify the ads as ads, and then click to close them, or use other techniques to either deal with them, all of which tax the user's intellectual focus in some way), then the user has effectively lost one dollar of time in order to deal with ads that might generate a few fractional pennies of display-ad revenue for the website owner. The problem of lost time can rapidly spiral out of control if malware accompanies the ads. This is discussed in more detail below.
Another important aspect is improving security; online advertising subjects users to a higher risk of infecting their devices with computer viruses than surfing pornography sites. In a high-profile case, malware was distributed through advertisements provided to YouTube by a malicious customer of Google's Doubleclick. In August 2015, a 0-day exploit in the Firefox browser was discovered in an advertisement on a website. When Forbes required users to disable ad blocking before viewing their website, those users were immediately served with pop-under malware.
Users who pay for total transferred bandwidth ("capped" or pay-for-usage connections) including most mobile users worldwide, have a direct financial benefit from filtering an ad before it is loaded. Streaming audio and video, even if they are not presented to the user interface, can rapidly consume gigabytes of transfer especially on a faster 4G connection. Since users without a data plan often pay by the megabyte, the cost of tolerating ads can be quite high. Even fixed connections are often subject to usage limits, especially the faster connections (100Mbit/s and up) which can quickly saturate a network if filled by streaming media. It is a known problem with most web browsers, including Firefox, that restoring sessions often plays multiple embedded ads at once. Using an advertisement blocker stops such behaviour, and makes it easier for people to use their computers and their Internet service.
Use of mobile and desktop ad blocking software designed to remove traditional advertising grew by 41% worldwide and by 48% in the U.S. between Q2 2014 and Q2 2015. As of Q2 2015, 45 million Americans were using ad blockers. In a survey research study released Q2 2016, MetaFacts reported 72 million Americans, 12.8 million adults in the UK, and 13.2 million adults in France were using ad blockers on their PCs, smartphones, or tablet computers. In March 2016, the Internet Advertising Bureau reported that UK adblocking was already at 22% among people over 18 years old.
As of 2015, advertisers and marketers look to involve their brands directly into the entertainment with native advertising and product placement (also known as brand integration or embedded marketing). An example of product placement would be for a soda pop manufacturer to pay a reality TV show producer to have the show's cast and host appear onscreen holding cans of the soft drink. Another common product placement is for an automotive manufacturer to give free cars to the producers of a TV show, in return for the show's producer depicting characters using these vehicles during the show.
One method of filtering is simply to block (or prevent autoplay of) Flash animation or image loading or Windows audio and video files. This can be done in most browsers easily and also improves security and privacy. This crude technological method is refined by numerous browser extensions. Every Internet browser handles this task differently, but, in general, one alters the options, preferences or application extensions to filter specific media types. An additional add-on is usually required to differentiate between ads and non-ads using the same technology, or between wanted and unwanted ads or behaviors. The more advanced ad blocking filter software allow fine-grained control of advertisements through features such as blacklists, whitelists, and regular expression filters. Certain security features also have the effect of disabling some ads. Some antivirus software can act as an ad blocker. Filtering by intermediaries such as ISP providers or national governments is increasingly common.
As of 2015, many web browsers block unsolicited pop-up ads automatically. Current versions of Konqueror and Internet Explorer also include content filtering support. Content filtering can be added to Firefox, Chromium-based browsers, Opera, Safari and other browsers with extensions such as AdBlock, Adblock Plus and uBlock, and a number of sources provide regularly updated filter lists. Adblock Plus (provided by the German software house Eyeo GmbH) is included in the freeware browser Maxthon from the Peoples Republic of China by default. Another method for filtering advertisements uses Cascading Style Sheets (CSS) rules to hide specific HTML and XHTML elements.
Hosts file and DNS manipulation
Most operating systems, even those which are aware of the Domain Name System (DNS), still offer backwards compatibility with a locally administered list of foreign hosts. This configuration, for historical reasons, is stored in a flat text file that by default contains very few hostnames and their associated IP addresses. Editing this hosts file is simple and effective because most DNS clients will read the local hosts file before querying a remote DNS server. Storing "blackhole" entries in the hosts file prevents the browser from accessing an ad server by manipulating the name resolution of the ad server to a local or nonexistent IP address (127.0.0.1 or 0.0.0.0 are typically used for IPv4 addresses). While simple to implement, these methods are also very easy for advertisers to circumvent. One method to circumvent this form of ad filtering is to load ads from servers with hard coded IP addresses, thus skipping name resolution altogether. Another method to evade this form of filtering is to load the advertisements from a server which also serves the main content; blocking name resolution of this server would also block the useful content of the site.
- Further information: hosts file.
Using a DNS sinkhole by manipulating the hosts file exploits the fact that most operating systems store a file with IP address, domain name pairs which is consulted by most browsers before using a DNS server to look up a domain name. By assigning the loopback address to each known ad server, the user directs traffic intended to reach each ad server to the local machine or to a virtual blackhole of /dev/null or bit bucket.
This method operates by filtering and changing records of a DNS cache. On most operating systems the domain name resolution always goes via DNS cache. By changing records within the cache or preventing records from entering the cache, programs are allowed or prevented from accessing domain names. The external programs monitor internal DNS cache and import DNS records from a file. As a part of the domain name resolution process, a DNS cache lookup is performed before contacting a DNS server. Thus its records take precedence over DNS server queries. Unlike the method of modifying a Hosts file, this method is more flexible as it uses more comprehensive data available from DNS cache records.
The filtering and selective blocking of DNS traffic can be performed by a DNS firewall which is configured to block DNS name resolution based on name patterns. A DNS firewall, such as Verigio DNS Firewall, can also block access to IP addresses for names not resolved via DNS. Thus prevent display of advertisements from servers accessed directly using their IP addresses.
Advertising can be blocked by using a DNS server which is configured to block access to domains or hostnames which are known to serve ads by spoofing the address. Users can choose to use an already modified DNS server or set up a dedicated device such as a Raspberry Pi themselves. Manipulating DNS is a widely employed method to manipulate what the end user sees from the Internet but can also be deployed locally for personal purposes. China runs its own root DNS and the EU has considered the same. Google has required their Google Public DNS be used for some applications on its Android devices. Accordingly, DNS addresses / domains used for advertising may be extremely vulnerable to a broad form of ad substitution whereby a domain that serves ads is entirely swapped out with one serving more local ads to some subset of users. This is especially likely in countries, notably Russia, India and China, where advertisers often refuse to pay for clicks or page views. DNS-level blocking of domains for non-commercial reasons is already common in China.
Devices such as AdTrap use hardware to block Internet advertising. Based on reviews of AdTrap, this device uses a Linux Kernel running a version of PrivProxy to block ads from video streaming, music streaming, and any Internet browser.
By external parties and internet providers
Internet providers, especially mobile operators, frequently offer proxies designed to reduce network traffic. Even when not targeted specifically at ad filtering, these proxy-based arrangements will block many types of advertisements that are too large or bandwidth-consuming, or that are otherwise deemed unsuited for the specific internet connection or target device. Many internet operators block some form of advertisements while at the same time injecting their own ads promoting their services and specials.
Economic consequences for online business
Some content providers have argued that widespread ad blocking results in decreased revenue to a website sustained by advertisements, and e-commerce-based businesses, where this blocking can be detected. Some have argued that since advertisers are ultimately paying for ads to increase their own revenues, eliminating ad blocking would only dilute the value per impression and drive down the price of advertising, arguing that like click fraud, impressions served to users who use ad blockers are of little to no value to advertisers. Consequently, they argue, eliminating ad blocking would not increase overall ad revenue to content providers in the long run.
Advertiser countermeasures and justifications
Some websites have taken counter-measures against ad blocking software, such as attempting to detect the presence of ad blockers and informing users of their views, or outright preventing users from accessing the content unless they disable the ad blocking software. There have been several arguments supporting and opposing the assertion that blocking ads is wrong. Some advertising companies have taken steps to protect their rights to conduct their business according to prevailing law. It has been suggested that in the European Union, the practice of websites scanning for ad blocking software may run afoul of the E-Privacy Directive. This suggestion has been debunked by experts, and has been also confirmed to rely on false assumptions by several industry representatives. Industry groups and the EU are still expected to establish clear guidelines on how to handle the issue in the future.
Advertiser network blocking
The PIPCU maintains an 'Infringing Website List' (IWL), a portal for digital advertisers to be informed of sites containing infringing content with the intention that they cease advertising on them. Sites are identified as infringing by rights holders and the list is not made available to the public. As of August 12, a freedom of information request from TorrentFreak revealed: 74 domains are subject to the advertiser blocking programme, of which of October 2014 only 2 domains had ever been removed from the list. 83 advertising companies with a UK presence are currently participating.
Working with the media and advertiser industry body, the Audit Bureau of Circulations (ABC) created a technology portal called 'Project Sunblock'. If the PIPCU do not receive a response from the website operators, the host or registrar of an allegedly infringing site, the site is added to the IWL via the Sunblock portal, which is then passed along to participating advertising networks for blacklisting. From June 2014 this technology allowed replacing the adverts of websites believed to be offering unauthorized content with warnings from the PIPCU.
This is an ongoing investigation and disclosure to the public domain would raise the profile of those sites unlawfully providing copyright material. This would enable individuals to visit the sites highlighted and unlawfully download copyright material and increase the scale of the loss. In the case of advertisers, public identification would increase the risk of harm to them by way of cyber attack or other means.— City of London Police
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