A German privacy watchdog has ordered Facebook to stop collecting data on WhatsApp users, a response to the introduction of a controversial data sharing scheme by the company in August.

In a statement on Tuesday, the Hamburg Commissioner for Data Protection and Freedom of Information said that it is “issuing an administrative order that prohibits Facebook with immediate effect to collect and store data of German WhatsApp users. Facebook is also ordered to delete all data that has already been forwarded by WhatsApp.”

Facebook bought WhatsApp for $19 billion in February 2014. However, the watchdog ruled that as both Facebook and WhatsApp operate independent companies that “both parties have publicly assured that data will not be shared between them,” and that the sharing scheme is therefore constitutes an infringement of national data protection law.”

The company argues that the sharing of data between the two services was solely to improve the quality of their services, such as helping users to find their friends across the platforms and using their collective data to reduce spam and fraudulent activity.

However, Johannes Caspar, the Hamburg Commissioner for Data Protection and Freedom of Information, ruled that Facebook failed to obtain permission from its users to collect WhatsApp data.

“This administrative order protects the data of about 35 million WhatsApp users in Germany. It has to be their decision, whether they want to connect their account with Facebook. Therefore, Facebook has to ask for their permission in advance. This has not happened,” he said.

A spokesperson for Facebook said that the company was planning to launch an appeal.

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