The winner candidate created a well funded structure to disseminate fake news through WhatsApp. There were demands to limit the ability for a individual to spread fake news, but WhatsApp/Facebook had deaf ears.

Here are a bunch of links from reputable sourcers:

https://www.bbc.com/news/av/world-latin-america-45769992/fig...

https://www.nytimes.com/2018/10/17/opinion/brazil-election-f...

https://www.theguardian.com/world/2018/oct/18/brazil-jair-bo...

https://www.independent.co.uk/news/world/americas/brazil-ele...

http://nymag.com/developing/2018/10/whatsapp-too-late-fake-n...

https://www.telegraph.co.uk/news/2018/10/18/jair-bolsonaro-a...