WhatsApp, the Facebook-owned messaging app, is one of the main tools that Brazilians use to keep in touch with friends and family, and do business. Increasingly, it is also a part of politics. A recent poll found that 44 percent of voters in Brazil use WhatsApp to read political and electoral information. Unfortunately, in the lead-up to the first round of the presidential election on Oct. 7, the app was used to spread alarming amounts of misinformation, rumors and false news.

With just a few weeks before the runoff vote on Oct. 28 between the far-right candidate Jair Bolsonaro and his left-wing opponent Fernando Haddad, there is still time for WhatsApp to make temporary changes to the platform to reduce the poisoning of Brazilian political life. The company must be decisive before it is too late.

There have been positive developments in the fight against false news in Brazil. Ours is one of 17 countries where Facebook has third-party fact checkers trying to weed out misinformation from the platform’s News Feed. Facebook and Google have also collaborated on an initiative called Comprova, gathering 24 Brazilian newsrooms to debunk misleading links, videos and images.

But these efforts seem to have pushed dirty campaigns elsewhere, in particular to WhatsApp, where activity consists of encrypted personal conversations and chat groups involving up to 256 people. Such chat groups are much harder to monitor than the Facebook News Feed or Google’s search results.