While plenty of outrageous stories about fast food prove to be true -- consider the person who sued McDonald's (MCD -0.05%) because her coffee was too hot -- others become huge news stories only to prove fake.

This is not a small problem, as learning that your beef supplier is using horse meat in its patties (which actually happened to Burger King (BKW.DL)) can damage a company's brand, even if it takes quick steps to correct the problem and no tainted meat was actually served. What consumers remember is "brand name + horse meat", not that it was more a media scandal than a true issue that actually affects customers.

This problem has become exacerbated by the Internet, which can turn rumors and hoaxes intro virtual truths. It can also make a localized problem seem like a brandwide issue. That happened with a singular New York City Yum! Brands (YUM -0.88%) KFC/Taco Bell location that led to a health inspector fired because, according to The New York Times, he gave it a passing grade days before videos surfaced of rats scurrying through the kitchen. In that case, the public narrative became "KFC infested with rats," not "one poorly run, franchised location infested with rats."

A number of fast-food stories have gone viral -- creating enormous negative publicity for the brands affected -- and later turned out to be complete hoaxes.

McDonald's coffee was the subject of a famous lawsuit. Source: McDonald's. 

1. Scarred girl not really shunned at KFC
In June 2014, a horrifying story of a disfigured young girl being asked to leave a Jackson, Mississippi KFC because her appearance was "disrupting our customers" went viral, The Daily Mail reported. The tale, told by the 3-year-old's grandmother, was later proven to be false by two separate investigations, though the grandmother has never recanted.

While the alleged insult might not have happened, the girl's injuries, which were caused by a dog mauling, were very real. They included the loss of her right eye, no longer being able to move that side of her face, and multiple broken bones, the New York Daily News reported when the later-disproved KFC story broke.

The fact that the slight to the injured child was untrue did not stop KFC from donating $30,000 to the Las Vegas doctor who agreed to treat her for free. Another $100,000 was donated via GoFundMe.com to help the girl, The Daily Mail reported.

So, while the story of the child being asked to leave the restaurant was a hoax that brought negative attention to KFC, the chain ultimately helped an innocent victim -- of a dog attack, not an insensitive KFC employee -- have a chance at a more normal life.

2. Is that a finger in my chili?
In 2005, before the Internet had fully realized its power to turn a false story "true" by making it so ubiquitous it can't be denied, Wendy's (WEN -1.07%) was scammed by a woman who claimed she found a human finger in her chili. The offending digit was eventually traced to an associate of fraudster Anna Ayala, who received four years in jail for the scam.

The extortion attempt cost the fast-food chain approximately $20 million in lost business, the New York Daily News reported.

3. Are the beef tacos made of beef?
When you label a product a beef taco, customers take it for granted that they are actually eating beef. Taco Bell, however, had been pulling a bit of a hoax on its customers for years, but the extent of the deception was not as bad as alleged by one widely reported lawsuit.

In a 2011 against Taco Bell, an Alabama law firm claimed the fast-food chain's meat was only 35% beef, Slate reported. The lawsuit brought a flurry of media stories and became fodder for late-night talk show hosts.

To answer the charges, Taco Bell provided an accounting of its "beef," which showed the 35% number to be a hoax, but might not have actually helped its case with consumers. The response said the 35% number is wrong -- Taco Bell's beef is actually 88% meat.

To explain the other 12%, Taco Bell posted a no-longer active page on its website that attempted to make light of the added ingredients, Slate reported.

"Caramel color and cocoa powder? Those sound like they belong in desserts!" the company stated before explaining that the cocoa "helps our seasoned beef maintain a rich color."

The company now has a policy of complete ingredient transparency and shows the full list of what goes into all its menu items on a Web page. So, in addition to 88% beef, anyone ordering a beef taco will get oats, soy lecithin, cocoa powder processed with alkali, something called trehalose, and a laundry list of other ingredients.