Corona warning app: Answers to frequently asked questions

Together with Deutsche Telekom, SAP is developing an app on behalf of the German government to help track infection chains in the COVID 19 pandemic. Learn more about the purpose and functionality of the software. An overview.

Environmental testing is a proven method of fighting epidemics. The first step is to find all infected people. After that, it is checked which group of people were in contact with the infected people and therefore might have been infected as well. The spread of the pathogen can then be contained by notifying all those affected, who should then go into quarantine.

This procedure is also used in the COVID 19 pandemic. Manual surveys of SARS-CoV-2 positives currently help to identify chains of infection. This procedure thus helps to reduce further infections by isolating contact persons at an early stage.

The app helps to curb the spread of COVID-19. It documents the digital encounter between two smartphones. This allows the app to quickly inform you if you had contact with a person diagnosed with COVID-19. The faster you receive this information, the lower the risk that many people will become infected. That is why the app is an effective means of curbing the corona virus, along with hygiene measures such as hand washing, social distancing and using everyday face masks. The Federal Government supports the app because it serves the protection and health of the community.

The Corona-Warn-App informs you if you have been near a person for a longer period who is later diagnosed with the corona virus. This enables you to quickly react accordingly, and not run the risk of unknowingly continuing to spread the virus. The manual process of tracking infections used to date is greatly accelerated with this digital assistance. The app runs on your smartphone while you go about your everyday activities. It recognises other smartphones nearby which also have the app enabled. The app then stores their random Bluetooth IDs (random IDs) for a limited period of time. These encrypted IDs (random IDs) do not allow connections to be made to you or your location.

The Corona-Warn-App uses Bluetooth technology to measure the distance and duration of the encounter between people who have installed the app. The smartphones "remember" encounters if the criteria determined by the RKI on distance and time are met. The devices then exchange temporary encrypted random IDs. If people using the app test positive for the corona virus, they can inform other users on a voluntary basis. Then the random IDs of the person diagnosed with COVID-19 are made available to all people who are using the Corona-Warn-App. If you have installed the app, it will check whether you have had contact with the person diagnosed with COVID-19 for you. This check is only performed on your smartphone. If it is positive, the app will display a warning. At no point in time does this procedure allow connections to be made to you or your location.

No. It is up to you to decide whether or not you want to use the app. Use of the Corona-Warn-App is voluntary, and is for your personal protection, as well as the protection of your fellow citizens. The aim of the Corona-Warn-App is to quickly identify and interrupt corona chains of infection. All users should be quickly and reliably informed about encounters with users of the app who have been diagnosed with COVID-19, and thus about a possible transmission of the virus. So they can quickly isolate themselves and get tested on a voluntary basis, and thereby help to curb the corona pandemic. You can delete the app at any time. This will also delete all of the information stored by the app.

Corona-Warn-App has now been downloaded more than 22 million times and is thus an active contribution to curbing the pandemic. The faster that people who have been diagnosed with COVID-19 and their contacts can be informed, the less the virus can spread. The app therefore helps you to protect yourself, your family, your friends and everyone around you. Without this technical assistance, staff at the health authorities would have to track each case personally. This is very time consuming, and it is often not even possible to find every single person, because who remembers everyone they have had contact with? The Corona-Warn-App solves these problems.

The Corona-Warn-App is a project commissioned by the Federal Government. The companies Deutsche Telekom and SAP have developed the application, based on a distributed software architecture. The Fraunhofer-Gesellschaft and the Helmholtz Center for Information Security (CISPA) provided advice and support.  In order to meet the requirements for data protection and data security, the Federal Office for Information Security (BSI) and the Federal Commissioner for Data Protection and Freedom of Information (BfDI) were also involved. The Robert Koch Institute plays a dual role in the Corona-Warn-App: it provides specialist expertise for the development of the app, and as publisher is also responsible for carefully checking the requirements for data protection and data security. 

The Corona-Warn-App is designed to be completely accessible to all. As many citizens should be able to use the app as possible, in order to ensure maximum protection against a renewed rapid spread of the virus. Therefore, the app can be used on the vast majority of current devices and with the common operating systems.

In order for an encounter to be rated as a potential exposure by the Corona-Warn-App, it must have been epidemiologically relevant. This means that there must have been a risk of infection. The Bluetooth technology used by the app allows it to work with two parameters: the duration of the encounter and the distance between the users. Both are calculated with the help of various measurements, and a threshold value is established. 

When contact occurs, the relevant users exchange temporary random IDs. These random IDs are stored exclusively on the smartphones of the relevant users who encountered each other for 14 days, and are compared with so-called diagnosis keys of those who are diagnosed with COVID-19, directly on the person’s smartphone. 

Exposure is defined in the app as an encounter with a person diagnosed with COVID-19, who exceeds a threshold value of various measurements. The people using the app are shown their risk status depending on these measurements. There are three types of status information: 

low risk

  • The person is informed that the exposure check of their exposure logging has shown no encounter with anyone who is known to have been diagnosed with COVID-19, or that any such encounters did not exceed the defined threshold value. 
  • The person is informed about generally applicable social distancing regulations and hygiene recommendations. 

increased risk

  • The person is informed that the exposure check of their exposure logging has shown an increased risk of infection, as they have encountered at least one person in the last 14 days who has been diagnosed with COVID-19. 
  • The person receives the recommended action to, if possible, go straight home or stay at home, as well as to contact either their general practitioner, the medical assistance hotline at 116 117 or the local health authorities and discuss the further course of action. 

unknown risk

  • If the risk identification has not been activated for long enough by the person, then no risk of infection can be calculated at this time. The person receives the status information "unknown risk". 

You will not receive a real-time warning when approaching a person diagnosed with COVID-19. The solution cannot enable a response in real time for data protection reasons. This would determine the identity of a person diagnosed with COVID-19 and violate corresponding protective rights. Your own smartphone has no information about who is infected. It only knows that it was near another smartphone on which a verified positive test result has been saved. Each person alone decides if a positive test result is shared or not. We are striving for an automated process where the result of "test positive" can be transferred to the smartphone as soon as it is reported and the person has actively authenticated themselves. However, every person who uses the app must always first manually change their status in the app to "positive" using a "sliding button". This kind of automated process is now possible today at 90 percent of German testing laboratories. In places where an automated process is still not possible, there is a manual process of calling an activation hotline to report positive tests, including verification of the test result.

The application runs in battery-saving background mode. When developing the solutions, we of course paid special attention to minimising the storage space required for the app itself and the contact with other smartphones stored. 

No, it isn't. The server only has the task of safely and efficiently sending the pseudonymised and authorised positive reports to all participants, so that an exposure check can take place on the users’ end devices, so locally. Of course no data is stored centrally.

The protection of your privacy is a top priority for the Federal Government. Therefore, when the Corona-Warn-App was being developed, it was ensured that the app meets the stringent German data protection requirements. In order to ensure that these requirements are met, both the Federal Commissioner for Data Protection and Freedom of Information (BfDI) and the Federal Office for Information Security (BSI) were involved in the development of the Corona-Warn-App right from the beginning. The BSI supports the development of the app on matters related to IT security. The BSI was therefore constantly examining the versions of the app provided by the developer teams during the development process, as well as the associated infrastructure, and providing advice on the security concept to be created. In addition, the complete source code on which the app is based has been made available to the public. This allows independent specialists from civil society to participate in the development and improvement of the app at any time, and to check it for weaknesses.

Your data is safe at all times. When you use the app, you will remain anonymous at all times. When you register to use the app, you do not have to provide any personal data (such as your name or e-mail address). The distributed data storage on the user devices themselves, as well as full pseudonymisation, guarantee a high level of data protection. All data – for example on encounters with other people using the app – is encrypted and stored exclusively on your own smartphone. Temporary random IDs are saved of other smartphones which have the app installed on them, if the RKI’s epidemiological criteria for the proximity and duration of an encounter are met. In the event of an infection, your own random IDs can be voluntarily shared, which enables other app users to have their risk calculated on their smartphones. With this data and the locally-stored data, it is possible for the app/smartphone (but not the server) to identify contact with a person diagnosed with COVID-19, and to warn the person accordingly. Data which can make a person identifiable, in particular location data, is not selected, used or stored. It is ensured that a person diagnosed with COVID-19 does not know which people are informed about an encounter. Contact people do not receive any information about the person diagnosed with COVID-19. Falsely reporting the infection status are prevented by technical and organisational measures. Neither the Federal Government, the Robert Koch Institute, nor other people using the app or the operators of the app stores can detect whether you report an infection with corona yourself, or whether you have had contact with a person diagnosed with COVID-19.

All countries of the European Union that offer a decentralized national warning app can use a special exchange server to participate in cross-border exchange of risk notifications. Ireland, Latvia and Germany started exchanging data in October 2020. Spain, Italy and Denmark are now also involved. Other countries will follow by the end of the year. 

A warning by the app is not sufficient on its own, but serves as a notification to get in touch with the healthcare system. If you receive a warning from the app, you should contact a medical specialist to clarify the further course of action. If you test positive for corona, you can get a medical certificate for sick leave and are entitled to continued salary payment. If the health authorities order you into quarantine, your employer continues to pay your salary/wages. Your employer will in turn be compensated for this by the health authorities. 

The "increased risk" warning by the Corona-Warn-App only informs the user that the close proximity and duration of an encounter with a person who has reported a positive test result via the app means that there is an increased risk of infection, and recommends that the user contact either their general practitioner, the medical assistance hotline at 116 117 or the local health authorities by telephone. The decisions on a medical certificate for sick leave and on ordering isolation at home (quarantine) are made by the consulting doctor and the relevant health authorities after an appropriate assessment.

FAQFind further frequently asked question on the official website of the open source project for the Corona Warning App.



Information related to the Covid-19 pandemic and the Corona Warn App.