Google has issued a fix for a bug that has affected, for the past couple of days, all Android-based apps that use the Exposure Notifications System, which includes many contact-tracing apps around the world and the NHS Covid-19 app.
The bug has caused delays in notifications being issued by the apps that are built on top of the Exposure Notifications System, an API that Google released jointly with Apple to help health services around the world develop COVID-19 contact-tracing apps.
The API enables developers to create privacy-preserving contact-tracing tools that rely on Bluetooth to exchange anonymous keys between smartphones, to easily warn users if they have been in contact with someone who later tested positive for coronavirus.
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The latest bug that was discovered means that some Android users who have been exposed to infected people might have experienced delays in being warned by the contact-tracing app that they are using. It doesn't appear that iOS devices have been affected by the issue.
First reports of the bug emerged earlier this week. Some users of the UK contact-tracing app, for example, described that a loading notification for the NHS COVID-19 app had appeared on their home screen when exposure notifications were turned on, and that they weren't able to swipe the notification away.
Google has confirmed that an issue was found in the Exposure Notifications System that was causing delays in the checking of potential exposures for those with apps installed. Because of a problem with key configuration, the apps had an issue downloading the diagnosis keys of infected users from their central servers.
A Google spokesperson told ZDNet: "We have issued a fix. It may take a few hours for devices to catch up, and in some cases we will work directly with developers to help with recovery. The issue did not cause the loss of any data or potential exposures."
During the time that the bug lasted, the contact-tracing apps that were affected continued to collect user keys and potential exposures. In most cases, delayed notifications will resume today; where they do not, some developer work will be needed to help the app catch up. Google has confirmed that it will be working with these developers to resolve the issue.
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For those who are still troubled by a stubborn loading notification on their home screen, re-booting the device might resolve the issue. Google, however, has urged users not to clear storage in their app, as this may cause a loss of data, and therefore potential exposures, from the interim period.
The bug affected all Android apps that leverage the API worldwide, but was not always visible. Users of the NHS COVID-19 app have been advised to re-start their phones if necessary, and reports of the issue also appeared in Germany's Corona-Warn app, as well as the Netherlands' CoronaMelder.
Google and Apple's API was released last April as part of an effort to build digital contact-tracing tools that protect privacy-by-design, and the system was adopted by many health authorities around the world. In the UK, the NHS's COVID-19 app has been downloaded more than 20.9 million times.