Ask HN: Which metadata WhatsApp has from users and groups?

WhatsApp just banned 100,000 Brazilian accounts: https://www.bloomberg.com/news/articles/2018-10-19/whatsapp-bans-more-than-100-000-accounts-in-brazil-election

This is a late response from WhatsApp. They are the main responsible for the easy spread of fake news in the current presidential elections: https://www.nytimes.com/2018/10/19/technology/whatsapp-brazil-presidential-election.html

Due to them, a extreme right candidate will be elected and Brazilian young democracy is in danger: https://www.economist.com/leaders/2018/09/20/jair-bolsonaro-latin-americas-latest-menace

I'd like to know what they know that allow them to ban these accounts.