Case study · 2018 to 2020 · filed 30 September 2026

Phones seen inside Catholic churches were used to find voters

A political group bought location data that came from ordinary phone apps, drew a line around Catholic churches, and sent ads to the people whose phones had been inside. The churches did not know.

The DÆTRAX team · privacy research

In July 2019 ThinkProgress reported that CatholicVote, a conservative political group, and Steve Bannon had used location data from phones that had been inside Roman Catholic churches in Dubuque, Iowa, in 2018 to send those people get-out-the-vote ads. The method is called geofencing: a boundary is drawn around a building, and the phones seen inside it are picked out for ads. In footage cut from a documentary, Bannon said: "Literally, they can tell who's been in a Catholic church and how frequently." The Archdiocese of Dubuque said it did not know its churches had been geofenced. ThinkProgress said it was not clear which broker supplied the data.

In November 2019 the group wrote on its own site that it had "identified 199,241 Catholics in Wisconsin who've been to church at least 3 times in the last 90 days", and that 91,373 of them were not registered to vote. Its president told Catholic News Service that the data came from third-party apps whose users had opted to share their location, and that the group was "merely a customer accessing the ad exchange along with thousands of other marketers". A reporter who covered the story told NPR that the churches "were not aware and had not consented in any way".

What it shows

Location data showed which phones had been inside a church, and that was enough to sort people by religion. The apps that gathered it had nothing to do with church. The data reached the group through the ad exchange, and the churches it was drawn around were never asked.

For your own record

Give your location only to apps that need it, and only while you use them. Ask the apps you use which companies receive your location, ad exchanges and data brokers included, and ask them to stop passing it on.

Start your record

More case studies

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Gloo A church marketing firm predicted who might be depressed, divorcing or addicted Gloo told churches it could predict who might have a marriage in trouble, depression or a drug addiction, from data it bought about Americans. After The Wall Street Journal asked, it stopped using mental health data and its main data supplier left.

Pray.com A prayer app took users' phonebooks and left them in open storage Pray.com uploaded the contact lists of users who let it, so it held people who had never used it. In 2020 researchers found those lists open to anyone, beside church member lists and donation records.