WhatsApp has collected the phone numbers of millions of people, even if they don't use the app themselves.

According to the Dutch data protection authority College Bescherming Persoonsgegevens (CBP), the company is now in illegal territory, the Volkskrant writes.

WhatsApp takes the complete address book of every user, it appears in the app's conditions to which every user has to agree. This means that phone numbers are also stored of contacts who do not use WhatsApp at all.

"In this way, you get your hands on details of people who never gave permission for that" says CBP-president Jacob Kohnstamm. The supervisor is still waiting on a reaction from a lawyer for WhatsApp.

If this is not satisfactory, the CBP can impose a penalty payment to force WhatsApp to change its modus operandi.