The good news: the app is coming. The long-awaited Corona warning app should be ready next Tuesday. However, there are not only 70 days between the originally scheduled start date in April and June 18, but also broken promises, chaotic communication and a publicly held dispute over the direction. Nevertheless, politicians and scientists have high hopes for technology – rightly? Answers to the most pressing questions:

What is the goal of the nationwide Corona app?


The app is designed to help keep the virus under control until a vaccine is developed. A second wave of infection could be imminent in autumn and winter. Then the app should relieve health authorities by automatically notifying contact persons of infected people. Ann Cathrin Riedel, Chair of the Association for Liberal Network Policy Load, warns of exaggerated expectations. “An app alone will never stop a virus,” she says. “Technology cannot solve social, medical or societal problems, but can only be a building block to contain the pandemic.”

How does the app work?

Countries like China and Israel rely on tracking, the German app is based on tracing. One letter makes a big difference: instead of storing whereabouts and movement profiles, the German Corona app only registers which devices come closer than two meters for at least 15 minutes. To do this, the smartphones scan the surroundings every few minutes and communicate with other mobile phones. Those who test positive for Covid-19 can release the locally stored data. Then contact persons are sent a push message to be tested. You will find out on which day the meeting took place, but not the exact time. In addition, the notification contains a risk value that is determined by four factors: how long ago the contact occurred, how long the encounter lasted, how strong the Bluetooth signal was and how the disease of the infected person progressed.


How are user data protected?

The app does not store any personal data, but is based on randomly generated, pseudonymous identification numbers that change at regular intervals. Developers and operators do not find out who is behind the ID and where users are. After two weeks, the contact diary is automatically deleted from the smartphone’s memory. The app only communicates with a central server once a day to retrieve the IDs of devices whose owners have reported that they are infected. Users can pause the tracing manually at any time.

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Health Minister Jens Spahn originally wanted to allow authorities to query the cell phone data of potentially infected people, but after protests he changed his plans.


(Photo: Sean Gallup / Getty Images)

In addition, the entire source code is open. Data protection experts and IT security researchers can independently check how the app works, which data is transferred and whether there are any weak points. Experts from the Chaos Computer Club and the Gesellschaft für Informatik consider the previously published program code to be exemplary. The software developer Henning Tillmann from the D64 network association describes the documentation as “exemplary” and praises the test process as “very detailed and well thought out”.

Who was involved in the development in Germany?

The federal government has commissioned Deutsche Telekom and software company SAP to build the app and operate the software architecture, which has to run in the background. Three scientific institutions were also involved: Fraunhofer, Helmholtz and Robert Koch Institutes. In addition, the Federal Data Protection Officer Ulrich Kelber (SPD) accompanied the development and will also ensure after the start of the app that the user’s privacy is preserved. The development of the app is said to have cost the federal government around 20 million euros. In addition, there are between 2.5 and 3.5 million euros per month to operate two multilingual telephone hotlines.


Could people be forced to use the app? The federal government emphasizes that the app is and should remain voluntary. Data protection experts also attach great importance to the app not being used as a form of pressure, for example by tying the entrance to certain rooms or trains to whether the visitor has installed it on the cell phone. Such a thing would not only be anti-data protection, but also discriminatory, says Federal Data Protection Commissioner Kelber: “I can only warn the owners of shops or public transport urgently: Don’t try it at all!”

How reliable does the app warn?

The distance between two devices is determined using the Bluetooth Low Energy (BLE) radio standard. In fact, the distance is estimated rather than measured: depending on the smartphone model, the signal strength differs; the cell phone works differently in the hand than in the pocket. In addition, panes of glass, walls and other obstacles can affect the result. “We don’t have to determine the exact distance at all, just whether the distance is above or below two meters,” says a SAP spokesman. Based on three so-called damping areas and the duration of the contact, the app calculates an infection risk. “This underlines how the specific distance moves into the background and the course of the encounter becomes more important.”


The accuracy of the data is “often relatively poor,” confirms computer science professor Stefan Brunthaler from the Bundeswehr University in Munich. He believes that “it is better to notify too many people of a potential infection than too few in an emergency.” Nevertheless, the success of the app will also depend on whether BLE can be configured precisely. If it warns too rarely, it does nothing. If too many push messages arrive, users will no longer take them seriously at some point.

How should misuse of the app be prevented?

To minimize false alarms, only people who actually carry the virus should be able to report as infected. Ideally, this is done using QR codes, which test laboratories provide in the event of a positive diagnosis. Users can then scan the code themselves and transfer their data. But not all laboratories have the technology necessary for this. Therefore, users have to verify themselves by telephone via a hotline in order to receive a tan. Psychologically trained employees should use test questions to find out whether they are dealing with an infected person or a troll who wants to abuse the system. At this point, the hotline is breaking the promise of anonymity, says Anke Domscheit-Berg, spokeswoman for the political group on the left. “To send a tan, you have to provide your employees with your own mobile number.”


Which smartphones is the app suitable for?

“There are old devices that do not support the new interface from Apple and Google,” says a SAP spokesman. “The app runs on iOS smartphones from iPhone 6s under iOS 13.5, with Android-based smartphones from Android 6.” Google Play Services is also required on Android. Some Chinese smartphones, such as new Huawei models, run without Google software due to the US trade embargo and are therefore not suitable for the app. Users should only download the application from the official Apple and Google app stores and be careful not to catch fake apps from third-party developers who want to tap data.

What experiences have other countries had?


Almost two dozen countries are already using warning apps against the corona virus. Some of them are very different from the German solution: some governments oblige their citizens to use them, others collect additional data and monitor users. A look at Australia and Austria is the most helpful, where apps have so far not played a central role in the fight against the pandemic. The initially euphoric reports from Singapore, whose Trace Together app has since become a role model for Germany, have not been confirmed.

How many people need to install the app for it to work successfully?

In recent months, it has repeatedly been said that 60 percent of the population would have to use a tracing app to interrupt infection chains. This presentation is based on statistical models from the University of Oxford, but is shortened. “Our models show that if around 60 percent of the population use the app, we can stop the epidemic,” write the scientists. But the sentence goes even further: “Even with a smaller proportion, we assume that the number of infections and deaths will decrease.”


According to the ARD Germany trend in June, 42 percent of those surveyed would be willing to do so, 39 percent do not want to install an app. The Nuremberg Institute for Market Decisions, on the other hand, has determined that 53 to 69 percent of people in Germany can imagine using the app.


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