Why internet filters fail.

Lessons learned from running an internet filter for the past year

Posted by Cam on April 30, 2020

One year ago, Truple launched a free android porn filter. It’s now been installed over 74 thousand times. We’ve learned a lot in the process of making and running the app, and we want to share the lessons that could help anyone trying to protect themselves or their loved ones online.

First of all, filter’s are extremely valuable. But you need to know what their limitations are and what protections they can actually provide. If you’re short on time, feel free to skip to the recommendations to understand when you should be using filters.

Internet filters have been around for decades and are the oldest form of online “protection”. Most of us have experienced them at school, the workplace, or public wifi locations like cafes or hotels. Installing a filter is typically the first attempt people make at gaining protection online. However under most circumstances filters alone are going to fail.

Our hope in sharing these insights is to help others achieve their goals more quickly and fail less often in the process.

Why filters fail

Filters fail primarily because they’re installed with the hope that they’ll block bad content from showing up on the screen, but filters don’t actually know anything about what’s on the screen.

What filters do understand, is internet traffic–typically DNS requests. They then guess what type of content is about to be displayed on the screen based on the traffic they see. Most of the time that traffic provides a very limited amount of information.

Reason #1: Website vs Webpage

Filters typically can’t tell what webpage you’re on. They can only tell what website you’re on. If you search on google for google.com?query=porn, all the filter will understand is that the website google.com was accessed. The filter won’t know that the webpage contained the term porn or anything else about the actual contents of the webpage. This used to not always be the case but is becoming more and more common as the internet (rightfully) becomes more private and encrypted.

Reason #2: Mixed Content

When filters recognize internet traffic for adultwebsite.com, they can typically guess that the content is bad and block it. But what about pinterest.com? instagram.com? reddit.com? Do those websites look bad? No they don’t. But they’re full of filth that’s easily found if sought after and can be thrust into your face if the website’s feed algorithm thinks you’ll click it (especially if you have in the past). We call these types of sites “mixed content” sites. Essentially they’re sites that are typically considered “acceptable” but they contained bad content.

You and your loved ones probably use many of these sites. Unfortunately, with filters you’re forced to decide whether to block mixed content websites entirely or leave them accessible. The latter will leave a gaping hole in the filter through which trash can be found, and the former will likely anger your kids and annoy you.

Reason #3: Limited to Internet Traffic

Filters only pay attention to internet traffic. They are unable to block any content accessed offline, through bluetooth, or a text message (think sexting).

Reason #4: Judgement call

Are lingerie websites acceptable? Swimwear websites? What about movies or tv shows that contain a few seconds of nudity?

With billions of websites out there, filters are forced to judge right vs wrong. Those who have created the filter designed it as best they could according to what they thought was right vs wrong. The filters judgement of what’s acceptable will never align perfectly with your own. The difference between what you want blocked and what the filter actually blocks will continue to sneak through.

Some filters are customizable and that can help with this. However once you realize the filter needs to be customized, the filter has already failed you because the bad content has already been accessed.

Reason #5: Annoying

Filters are annoying. You’ll regularly find the need to manually block and whitelist websites. Unfortunately if you’re blocking it manually, that means the filter already failed you and the content was already viewed.

To make matters worse, filters can also interfere with websites/apps and prevent them from working properly. The filter creators will typically test for this with commonly used apps, but for less commonly used apps (like ones you use for work or school) the filter won’t have been tested to ensure compatibility.

Reason #6: Filters don’t educate

Filter’s don’t teach self control. Once you gain access to a device that is unrestricted, you won’t have any better understanding of how to avoid bad content. You’ll just be left without any protection.

Reason #7: Filters struggle to keep up

There are billions of websites and every single day those websites change. Filters are always playing catch up.

Some malicious adult websites are aware of filters and have started creating copy websites on a regular basis in order to make their content available to users behind a filter. One week it’ll be accessible at badwebsite23456.com, then the next week it’s accessible at badwebsite53455.com, and so on.

Reason #8: Foreign languages

Filters built by engineers who speak English will most likely know to block adultwebsite.com. But what about voksenwebsted.com? Voksenwebsted is the Danish word for adult website after all. There are 6000+ languages in the world today. Even with the advancements of artificial intelligence, most filters struggle at translating and categorizing content in less common languages.

Reason #9: VPNs, Proxies, mobile hotspots,

There are numerous ways to bypass filters, including VPNs, proxies, using ip addresses directly, or the tor network just to name a few.

Reason #10: ISP compatibility issues

Some internet providers/networks force you to use their DNS servers. When filtering is implemented through DNS (which is the most common way), this means the filter will simply not work when you’re connected to their networks. This most commonly occurs with public wifi connections at hotels or cafes, but can also occur on school and workplace wifi connections and some mobile data connections as well.

Reason #11: More than just porn

There are more types of bad content accessed through tech devices than just pornography. Cyberbullying, online gambling, extreme violence, buying & selling drugs, communities encouraging suicide, racisms, and bigotry are just to name a few.


We recommend filters under the following circumstances:

  1. To protect against accidental exposure in environments where the individuals using the device will not be tempted to view or seek out bad/pornographic content.
  2. To prevent access to malicious websites that will attempt to steal your identity or financial information
  3. As a supplement to our Screenshot Accountability product.

Screenshot Accountability

The root of the issue with filters is they pay attention to the wrong thing. You aren’t concerned about internet traffic. You are concerned about the content being displayed on the screen. This is why our Screenshot Accountability product works so well. It goes directly to the source and shares random screenshots with a trusted friend or loved one. You and that trusted friend can decide whats acceptable or isn’t. Access to the premium features of the web filter is included in every screenshot accountability subscription. Learn more at https://truple.io.

Also, at https://app.truple.io/filter we provide a list of filter resources enabling you to add filtering to most devices in your home for free.

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