A new analysis by the human rights organization Global Witness revealed that YouTube and Facebook are allowing disinformation about Brazil's election campaign to spread, adding to the anger in an already polarized and violent race.

During an election season characterized by the feud between far-right incumbent Jair Bolsonaro and his leftist rival, former President Luiz Inacio Lula da Silva, the NGO prepared a series of purposefully false advertising.

Some of the spoof commercials advised people not to vote; others, including Bolsonaro, questioned the legitimacy of the election; and a few supplied an incorrect date for the votes.

To the NGO's surprise, YouTube approved all of them to run and Facebook approved half, Global Witness said, stressing that it withdrew the ads before they were published to avoid spreading confusion.

Read next: Bolsonaro and da Silva trade insults in first debate

“It’s frankly shocking that these massive firms with the technological prowess they clearly have, are unable to weed out such blatant disinformation being pushed onto their users,” said Jon Lloyd, Global Witness’s senior advisor.

“If it wasn’t already obvious it should now be undeniable to even the biggest skeptic – social media firms are fundamentally failing in their responsibility to stop democratic processes being undermined by false, misleading, and purposeful deceit.”  

According to the group, Facebook approved all 11 of its ads in late July and early August, two months before the elections for president, Congress, and governors and legislatures in 27 states.

A month before the 2 October elections, half of the commercials were allowed in a second test, and the same amount was approved after Lula won the first-round election with 48.4% to Bolsonaro's 43.2%. According to Global Witness, some of the advertising that passed Facebook's checks had been rejected in earlier tests.

That last wave, which took place between October 11 and 13, was expanded to include YouTube "and every single ad tested was authorized by the Google-owned platform," including several that falsely claimed the run-off ballot would be moved from October 30 to October 31.

Read next: Brazilian supreme court Judge orders blocking of Telegram in country - Reports

In response, a Meta representative claimed that the company invests "substantial resources" in election security and rejected 135,000 Brazil-related ad submissions between August 16 and September 30. “These reports were based on a very small sample of ads,” they said of the Global Witness submissions, “and are not representative given the number of political ads we review daily across the world.”

On its part, YouTube said it “reviewed the ads in question and removed those that violated our policies,” although the Global Witness report showed all the ads submitted were approved by the Google-owned site.