Pope Francis, who earlier this year was reported - falsely - to have endorsed Donald Trump for US president, has warned about the dangers of fake news.
In an interview published in the Belgian Catholic weekly Tertio, Francis repeated a frequent warning of his that the media can fall prey to spreading slander, scandal, defamation and disinformation.
He said: "Disinformation is probably the greatest damage that the media can do, as opinion is guided in one direction, neglecting the other part of the truth."
Francis was a victim of fake news spread on social media, including the false claim that he had endorsed Mr Trump.
Popes do not endorse political candidates, though he urged Catholic voters to "study the proposals well, pray and choose in conscience".
Several large German companies, including BMW, have pulled their ads from US-based news and opinion website Breitbart due to concerns about its content, following a similar move by cereal maker Kellogg's.
The German boycott was spurred by a social media campaign using the hashtag #KeinGeldFuerRechts, which translates as No Money for the Right.
The campaign urges companies to stop paying for ads on sites considered to promote racist and nationalist ideas.
Deutsche Telekom said it regretted advertising on Breitbart, saying the ads had not been placed there intentionally and it would blacklist the site from future campaigns.
The telecoms giant said it "absolutely doesn't tolerate discriminatory actions or statements".
Supermarket group REWE, BMW, Telefonica Deutschland, which is the mobile operator of O2, and restaurant chain Vapiano also said they had stopped advertising on Breitbart and distanced themselves from the site.
"The positions held by Breitbart.com contrast with Vapiano's values, such as openness and tolerance," the company said.
Last week's decision by Kellogg's to stop advertising on Breitbart prompted the website in turn to call for a boycott of the cereal maker.
Breitbart reportedly plans to open sites in France and Germany soon.
Germany, which is expected to hold a general election in September, introduced restrictions on free speech after the Second World War to prevent a revival of Nazi ideology.