"WhatsApp will take legal action against those we determine are engaged in or assisting others in abuse… even if that determination is based on information solely available to us off our platform," the company warned in an ominous FAQ entry posted on Monday.

Off-platform evidence of ban-worthy behaviors, including "automated or bulk messaging, or non-personal use," could trigger not just "technological enforcement" but legal repercussions, the post warned – and woe betide those users caught bragging off-platform about their ability to evade the rules. WhatsApp boasted it can ban users "based on machine-learning classifiers" alone, and will continue to do so. 

While the announcement repeatedly cited bulk messaging and spamming as key abusive behaviors, users have been banned for less – merely adding people not on a user's contact list to a group chat or sending messages to unknown users has gotten people booted from the platform.