Meta, the company behind Facebook, has filed a lawsuit against three Chinese companies, claiming they stole the passwords of users who logged in to their accounts using unofficial WhatsApp applications.

According to Meta, WhatsApp clients from three Chinese companies – HeyMods, Highlight Mobi and HeyWhatsApp – running under various names were available for download from the Play Store, APK Pure and several other app stores from May this year. Their developers promised that anyone who installed the apps would get various extra features.

But Meta has discovered that the apps steal users’ login details to gain access to their accounts, which they then use to send unsolicited and malicious messages.

Bleeping Computer reports that one of the apps in the lawsuit, WhatsPlus, alone had more than a million downloads in the Play store alone before Google made it unavailable.

Meta’s head of WhatsApp, Will Catchart, warned all users back in July that if they want to do well for themselves, they should only give their login details to the official WhatsApp app.