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The ad blocker battle pitting consumers and privacy advocates against big media companies heated up last week when Yahoo issued an ultimatum to some customers: Stop using software that limits ads or forget about using Yahoo Mail.

Yahoo entered the contentious debate over ad blockers by testing听听to lock out mail听customers using the popular extension AdBlock. While the test doesn't affect all Yahoo users and may not be permanent,听it points to听how threatening ad blocking technology has become to Internet companies that rely heavily on online advertising revenue.听

Ab blockers have been around for years but gained new prominence and popularity this year when Apple to ad blocking apps in September. Compounding the list of big tech names in the fray, earlier this month Firefox broke new ground by introducing an听听for the private-mode on its browser.

That kind of built-in support for blocking isn't sitting well with听major Web publishers, who have听听in an effort to blunt the development of technology designed to make the Internet a more ad-free environment.听

But the issues around ad blockers are much more nuanced than the tug-of-war between听impatient consumers who don't want to see pop-ups and publishers that want to hold onto profits. It's also about privacy, security, and the continued ability to access free content on the Web.

What鈥檚 an ad blocker?

An ad blocker is software, such as an application or extension, that prevents Web browsers from displaying advertisements. Some of the most popular ad blockers are , , , and .

Privacy nonprofit Electronic Frontier Foundation developed , a browser extension that gives users control over which specific third-parties 鈥� thus ad companies 鈥� are allowed to track them across websites.

There are varying estimates for how widespread ad blocker use is, but AdBlock boasts 200 million downloads from the Google Chrome Web Store.

Native advertising is where blocking get a little less clear. Native ads are presented in a similar format as a publisher's original content in a bid to be less intrusive. Depending on whether the ad is published through the site's platform or served through the ad company, the native ad by ad blockers.

What are the key issues?

At its most basic level, the debate consists of two camps. One side for consumers to block ads because it deprives publishers and advertisers of ad revenue. The other side argues that ad blockers are necessary to combat ads that intrude on their browsing experience.

Many ad blocking proponents use the software to opt-out of that advertisers rely on to target ads and model consumer behavior.

What鈥檚 at stake?

For those against ad blockers, the stakes are monetary.

Online advertising totaled , according to the Interactive Advertising Bureau. A report estimates that ad blockers will deprive advertisers of $22 billion in 2015, more than 40 percent more than in 2014.

That could and blogs, which can rely heavily on online advertising to turn a profit. argue that adapting to the world of ad blockers by creating less-intrusive ads puts an on publishers. Some publishers are even opting for .

Making the issue even more complex, some big companies could stand to gain by offering ad blockers to limit their competitors' ads.

Google controls of the online advertising market, dominating desktop browser-generated revenue. But on mobile, Apple's Safari is the . , means Apple has a good amount to gain from undercutting Google's profit from online ads by introducing ad blockers for mobile.

For-profit ad blockers, too, complicate the issue. Adblock Plus, which is free to download, works by "听of companies whose ads will not be blocked by the application, charging companies to be on the list as long as their ads pass AdBlock Plus' criteria. The creator of the most popular ad blocker in Apple's App Store pulled his paid blocker from the store, profiting from squashing others' content.

For those in favor of ad blocking, speed and privacy are at stake.

Many sites with ads because the ads are coming from multiple sources. Ad blockers can help speed up a site by blocking the elements that slow down the page from loading. Some people in this camp argue that ad blocking is ethical because the methods publishers use for 听Many also argue that online ad tracking has become too invasive.听

For instance, some privacy advocates argue that ad tracking can use information collected to create of a person, which can be difficult for consumers to change. Edward Snowden recently weighed in, arguing that if online ads are served over an insecure connection, that can be a way to with malware.

Is there an alternative way?

Right now, there are few ways to prevent Internet tracking without ad blockers. Vigilant users can try the anonymizing Web browser Tor for an added layer of privacy, as one woman did to from targeted advertising. 听

support a feature called "," which, if enabled, requests that any websites visited do not track the user. But not every website will comply with the request. The feature is part of a larger Do Not Track companies and privacy organizations that seek to get websites to honor the requests.

The EFF听 for Do Not Track earlier this summer 鈥� if publishers adhere to Do Not Track requests and compel the advertisers they use to do so as well, the publishers get verified by the EFF. 听So far, no advertising agencies have taken the EFF up on it.

The听Federal Communications Commission recently regulations that would force providers like Google and Mozilla to honor Do Not Track requests.

As a result, privacy advocates to enforce Do Not Track. According to听John Simpson of Consumer Watchdog, "Requiring that Do Not Track requests be honored is a simple way to give people necessary control of their information and is in no way an attempt to regulate the content of the Internet."

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