Despite massive pressure to change its policies, Facebook just announced that it will continue to allow politicians to lie in paid ads and will not limit microtargeting (though users can now opt-out of political ads and custom ad targeting).

While there has been a lot of news recently about microtargeting – in particular when it comes to political ads – many people are still unfamiliar with how microtargeting works. Advertisers like Facebook collect troves of information about individuals and in turn use that data to reach and influence advertisers’ target audience.

Microtargeting might help you discover your new favorite shampoo, but when it comes to political advertising, it can be especially problematic as it contributes to the spread of misinformation and digital manipulation – essentially jeopardizing the democratic process. There are lots of ways that this happens. Sometimes, an electoral campaign may run an official ad that’s problematic. More often, outside groups may run misinformation campaigns using microtargeting to polarize people and influence elections.

Facebook defines political ads as those that are about, paid for by, or on behalf of a candidate for public office, or that otherwise advocate for a specific electoral outcome. That’s fairly straightforward, but Facebook also extends its definition to ads about social issues as well as those that are generally about a referendum or encourage general voter participation.

So how does microtargeting on Facebook work? Targeted ads use data to segment audiences into different categories: demographic, geographic, income, and endless others. This data may be either collected directly, bought from another party, or inferred about an individual. Microtargeting combines different sets of personal data to segment and target users in increasingly invasive ways.

There are many ways that audiences can be segmented and targeted via Facebook’s ad platform. Microtargeting allows advertisers to more precisely tailor their messages to specific audience segments – but it also poses some serious threats to privacy and corporate accountability. Facebook has several tools for targeting, including:

Custom audiences allow advertisers to upload their lists and create a specific audience they want to reach (or exclude). On Facebook, custom audiences can include people identified through web traffic via a pixel embedded on websites outside of Facebook. This means that even when you’re browsing another website, that information could end up back at Facebook. It also means that any company or organization that has your email address can find you and target you with ads on Facebook. For political campaigns, they can also upload the voter file they have purchased and match other information they have about you to your voting history. In January, Facebook announced that it will allow users to control which ads they see based on custom audience targeting.

Look-alike audiences is a Facebook tool that allows advertisers to upload a list or select a custom audience of people and then, using a complex algorithm, create an audience that is likely to be just as receptive to the messaging as the initial custom audience. For instance, an advertiser may choose a custom audience (“people who like the Beach Boys”) and then use Facebook’s look-alike tool – powered by a black box algorithm – to target people with similar characteristics beyond that audience.

These are just two of the many ways that Facebook, and other ad platforms, allows advertisers to segment their audiences. Advertisers can also target based on people’s interests and demographics.

The role of microtargeting in political advertising has generated attention as tech companies wrestle with the most effective ways to curb disinformation in the context of elections. For months, Facebook has drawn criticism over Mark Zuckerberg’s announcement that ads placed by candidates would not be fact-checked. While political organizations, including 527s – political groups or parties that can raise unlimited funds and are not regulated by the Federal Election Commission (FEC) – should theoretically be subject to Facebook’s fact checking, these political groups are still getting away with blatant falsehoods in microtargeted ads.

Microtargeting has profound consequences for society even beyond political ads, as it can allow for wide-spread discrimination. Our friends at Ranking Digital Rights have called for platforms to disable ad targeting by default, so people would have to opt-in to receive targeted ads.

Political speech is critical to democratic discourse, but in contrast to broadcast advertisements, microtargeted digital ads keep ideas from being debated in the open, and fiction parades as fact. Because of that, Mozilla is calling on online platforms to help reduce voter manipulation by limiting political ads to a scale where they facilitate a public discourse.