Ad Filtering


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Ad filtering or ad blocking is removing or altering advertising content in a webpage. Advertising can exist in a variety of forms including pictures, animations, embedded audio and video, text, or pop-up windows. Very often it employs autoplay of audio and video.

It is a known problem with most web browsers that restoring sessions often plays multiple embedded ads at once. All browsers offer some solution to the problem, either by targeting technologies (Flash/Shockwave, Window Media files, etc.) that are used to deliver ads, targeting URLs that are the source of ads, or targeting behavior characteristic of ads (such as the use of HTML5 autoplay of both audio and video).

An extremely common 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. This crude technological method is refined by numerous browser extensions. In general one alters the options, preferences or application extensions to filter specific media types, but an additional add-on is required to differentiate between ads and non-ads using the same technology, or between wanted and unwanted ads or behaviors. The more advanced filters 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 ad blocker, including some freeware such as Avast. Ironically, some of this freeware itself runs ads, and instructions on how to block those are common on the web. For instance, Avast’s ads to upgrade itself to the paid version which are easily disabled.

Filtering by intermediaries such as providers or national governments is increasingly common. To users, the benefits of ad blocking include quicker loading and cleaner looking Web pages free from advertisements, 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 minimal amounts of energy. 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. The extent of unlimited bandwidth plans is often grossly over-estimated by US and European users and advertisers. This problem affects other countries, especially those with bandwidth limitations on their global Internet connections, or those that have poor regulatory or effective monopoly providers.

To advertisers, the benefits include not angering or annoying users into blocking, defaming or boycotting their products or websites. Few advertisers actually intend to anger end users. Very sophisticated filtering and anti-spam techniques can involve active defenses which can shut down an advertiser’s domains or brokers, ban them from searches or target them for other countermeasures. Some countries have even considered banning the use of certain ports, e.g. South Korea’s proposed ban on port 25 used by SMTP. Future countermeasures would be likely to include bans on ads South Koreans are unlikely to want or even ad brokering services. Ad substituting is also a legal and common practice already, for instance in Canadian cable TV where regulations permit showing a Canadian channel with Canadian ads instead of a US channel with US ads, where both are broadcasting the show simultaneously – this practice has spread to the web with some cable Internet providers uniformly substituting foreign ads, for local ones for which they receive a share of the revenue. Avoiding national, provider or technological interference with their ads is a priority for advertisers and especially brokers of advertising, to whom it could be fatal.

A number of website operators, who use online advertisements to fund the hosting of their websites, argue that the use of ad-blocking software risks cutting off their revenue stream. While some websites have successfully implemented subscription and membership based systems for revenue, the majority of websites today rely on online advertising to function. 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. Regardless of the morality of the matter, image loading and audio/video loading has always been under the direct control of the browser since the early days of the web. No advertiser can argue reasonably that they expected unfettered access to user ears and eyes when they chose to advertise on the web and the technology will not disappear nor be restricted legally in any developed country. Accordingly ad filtering will likely remain an arms race resolved by technological rather than legal supremacy.

Almost all modern web browsers block unsolicited pop-up ads by default. Some also include content filtering, which prevents external files such as images or JavaScript files from loading. Content filtering can be added to some browsers as extensions or plugins and a number of sources provide regularly updated filter lists. There are other more complex means of ad filtering such as using CSS rules to hide specific HTML and XHTML elements. A number of external applications offer ad filtering as a primary or additional feature. A traditional solution is to customize an HTTP proxy (or web proxy) to filter content. These programs work by caching and filtering content before it is displayed in a user’s browser. This provides an opportunity to remove not only ads but also content which may be offensive, inappropriate, or simply junk. The main advantage of the method is freedom from implementation limitations (browser, working techniques) and centralization of control (the proxy can be used by many users). The major drawback is that the proxy sees only raw content and thus it’s difficult to handle JavaScript-generated content.

Morally, while some argue that domain name holders are owners of property (and have been found to have such rights in most developed countries), it has also been one of the web’s most basic features that DNS (Domain Name Services — used to convert a computer’s host name into an IP address) can be localized and run on client, LAN, provider, and national services. China, for instance, 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.

Internet providers, especially mobile operators do frequently offer proxies designed to reduce network traffic. Even when not targeted at ad filtering specifically these will block many types of advertisements that are too large, bandwidth consuming or otherwise deemed unsuited for the specific internet connection or target device.

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