Denmark’s Tax Agency and public entity Udbetaling Danmark are potentially conducting surveillance of private citizens by using phone geolocation data to look for potential tax evasion according to Schürmann, professor at the IT University of Copenhagen and head of the national Centre for Cybersecurity.

In comments to newswire Ritzau, Schürmann stressed that he was speaking in general terms about the issue because he is not familiar with the origin of the data and what it is being used for, since the Tax Ministry has not made this information public.

Generally speaking, however, Danish tax authorities to are able collect data which can tell them whether you have checked your tax statement from you own address or from elsewhere, he said.

“If they have information about your location, they also know everything about where you were when you checked your tax statement and so on,” he said.

“Why do they need that type of information? I can’t see [why]. But if you don’t log in from your normal address, maybe there’s something interesting [about it],” he said.

The Danish Tax Agency (Skat) and Udbetaling Danmark, the state entity which administrates social welfare payments, both use geolocation data to check up on tax deductions, subsidies and benefits, newspaper Politiken reported earlier this week.

According to the newspaper, the public authorities do not collect location data themselves but more probably purchase it from telecommunications companies, websites or apps that collect it.

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Both Skat and Udbetaling Danmark are within their rights to use data from publicly available sources.

While the police and intelligence agency PET are possible buyers of tracking data, Schürmann said he had never heard other authorities doing this.

“There have been many discussions over the extent to which the police and PET should have access to data that is actually very protected,” he said.

Geolocation data can be used to reveal whether someone who, for example, received unemployment benefits has been abroad, thereby breaching rules, Politiken wrote as an example of how tracking data could be used.

Schürmann also said that it is completely normal for telecommunications companies to know exactly where an individual’s phone is at any given time.

IT systems can meanwhile recognise your location when you login to platforms using Denmark’s digital ID MitID, he said.

The use of geolocation data by authorities raises a central question, however, according to the professor.

“Do they have access to some of this data, or do they buy all data for an entire year?”, he said to Ritzau.

The Danish Tax Authority (Skattestyrelsen) legal director, Katrine Ledam Rasmussen, told Ritzau on Tuesday that the authority only makes public “general information” related to the agency’s checks.

That is because “more detailed information could be abused by businesses and individuals who intentionally try to break the rules and avoid paying correct taxes,” she said.