Facebook has been ordered to stop collecting and storing data on WhatsApp users in Germany in a major privacy blow for the company.
WhatsApp announced in August that it planned to start moving user data to Facebook following the merging of the two firms in February 2014.
The data sharing deal was dealt its first regulatory challenge on Tuesday courtesy of Germany, which has said that the deal is "misleading" for users and "constitutes an infringement of national data protection law" given that WhatsApp and Facebook said publicly that data will not be shared between them when the merger took place.
Germany's privacy watchdog said in a statement: "Such an exchange is only admissible if both companies, the one that provides the data (WhatsApp) as well as the receiving company (Facebook), have established a legal basis for doing so.
"Facebook, however, has neither obtained an effective approval from the WhatsApp users, nor does a legal basis for the data reception exist."
Johannes Caspar, Hamburg Commissioner for Data Protection and Freedom of Information, added: "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.
"In addition, there are many millions of people whose contact details were uploaded to WhatsApp from the user's address books, although they might not even have a connection to Facebook or WhatsApp. According to Facebook, this gigantic amount of data has not yet been collected.
"Facebook's answer, that this has merely not been done for the time being, is cause for concern that the gravity of the data protection breach will have a much more severe impact."
Facebook had not responded to a request for comment on the ruling at the time of publication.
This isn't the first time the deal has been challenged. The UK Information Commissioner's Office has said it will cast its eye over the data sharing plans to make sure WhatsApp is being fully transparent about the controversial move.
Privacy campaigners have also spoken out. The EFF described the move as "a clear threat to users’ control of how their WhatsApp data is shared and used".
AlphaBay users had flocked to Hansa after it was closed down - not realising it had already been taken over by Dutch police
Microsoft closes in on $100bn annual revenues with sales weighing-in at $23.3bn
Moves to take down cyber-squatted domains reveals Fancy Bear hacking network, claims Microsoft
Intel claims 'world first' in artificial intelligence that can be plugged-in almost anywhere