McDonald's urban legends
There are many urban legends about McDonald's, the global United States-based fast food chain. McDonald's has a very high profile in much of the world, and, especially within the anti-globalization movement, is sometimes held as a symbol of the negative impacts of globalization.
Many large companies have been the subject of rumors that they substitute unusual and unethical substances in their products, usually to save a few cents per serving. McDonald's is not immune to such claims. The following is a list of the most popular rumors about their food.
One common thread that ties many stories like these together, is the fact that they were not reported to the easily accessible mainstream media, police, medical services, or even government-run food or health inspection agencies, such as the United States Food and Drug Administration (FDA). These agencies and services are legally obliged to act on such extreme cases.
There has been a rumor that McDonald's hamburgers are made of worm meat. This rumor dates back to at least 1978, or possibly earlier. One account of the story claims it was dug up by 60 Minutes. The show has never aired a segment on this or any similar theme. Other variants have credited other investigative journalism shows for the "shocker". Some versions of the tale have it being revealed in a talk show chat with company CEOs, though it is unlikely that business people would even be interesting enough to be booked and appear on a talk show.
However, neither McDonald's nor any other restaurant would use worms, for the simple reason that worms cost more per unit of weight . While worm meat is considered very nutritious , and contains no gristle, to use worms as filler would be more expensive than using actual beef. McDonald's has gigantic shipments of meat it regularly orders from cattle farmers. If one was to suppose that worm meat were used, one must justify the small proportion of the U.S. population involved in worm farming. "At an Atlanta press conference, McDonald's officials, backed by a regional officer of the U.S. Department of Agriculture, denounced the rumors as "completely unfounded and unsubstantiated", and swore that the company's hamburgers contain nothing but beef". From Newsweek, November 27, 1978. McDonald's released a letter from the U.S. Secretary of Agriculture in 1982, attesting to McDonald's burger's pure beef content. It was used as proof in a rebuttal press conference on October 1 of that year, against the rumor. 
It is a rumor that their hamburgers are made from soy.
There is another rumor that McDonald's hamburgers are made of kangaroo meat. Origins and details are similar to the above rumor about worm meat. Kangaroos are regularly killed en-masse in Australia, as they are considered a pest when in large numbers, and their carcasses are essentially useless. 
However, the cost of setting up a major operation to transport this meat thousands of kilometres from Australia would theoretically be astronomical, and would be represented in the consumer's final price for purchasing the burger at a McDonald's restaurant. To set up a case against McDonald's on this, one would have to justify what McDonald's does with the gigantic shipments of meat it regularly orders from cattle farmers. If one was to suppose that kangaroo meat was used, one would have to question why there aren't obvious bulk quantities of kangaroo meat coming into the US from Australia. However, this explanation had yet to provide more localized versions, that only McDonald's in Australia use kangaroo meat.
Kangaroo meat, properly processed is more expensive in Australia than Beef. Kangaroo meat is also healthier, containing less fat and more protein, and is on the menus of many upper-class restaurants in Australia and abroad. Another fact is that if MacDonald's really used Kangaroo meat they meat would be really hard to digest.
Another popular rumour is that McDonald's widely uses cow eyeballs in its products, permitting it to brand them as "100% beef". However, the USDA mandates that all beef by-products, including cow eyeballs, be appropriately labelled. McDonald's, however, has asserted that its products contain "100% pure USDA inspected beef; no additives, no fillers, no extenders." In addition, cow eyeballs are actually more expensive than real beef, allegedly due to demand from scientific institutions for experiments.  Also, a cow eyeball weighs only about an ounce, so it would take too many eyeballs to make up one burger to be worthwhile.
Mutant laboratory meat
Around March, 2000, an Internet rumor spread via e-mail in Brazil "revealed" that McDonald's meat was actually made from a genetically modified "thing" maintained in laboratory. The e-mail stated that "the few who saw it assure it is a very unpleasant sight: they have no limbs or horns, no bones (undeveloped cartilage instead), no eyes, no tail and no fur; its head is about the size of a tennis ball; they are fed through tubes connected directly into their stomach". 
The e-mail carries on saying that "some irreversible health damage can be done by eating this meat, resulting in diseases who manifest themselves in a way similar to AIDS, and have symptoms related to Alzheimer's Disease" and ends encouraging the reader to boycott McDonald's until it sells actual beef.
The "discovery" was credited to researchers from the University of Michigan, although there's no official claims from anyone who actually works there.
Some analyzers claim that the origins of this rumor are from Portugual, because of the use of the word SIDA instead of AIDS (in Brazil they say AIDS too) and the word "facto" when in Brazil "fato" is used.
This urban legend is supposedly a variation of the "Frankenchicken Legend". According to this rumor, the chicken sold by Kentucky Fried Chicken are "things" genetically modified which have no beak, legs or feathers.
Beef tallow in french fries
Although McDonald's claimed it switched to vegetable oil in the United States in 1990, and would no longer use beef tallow to fry its french fries, it was rumored to the dismay of vegetarians and Hindus that the practice of using beef tallow to fry french fries remained.
McDonald's switched to using vegetable oil instead in 1990, in an attempt to market its french fries as being healthier than in the past by reducing the saturated fat content. However, the company retained beef extract as a flavoring ingredient, because customers preferred the flavor of beef tallow. Therefore, the french fries were not vegetarian; however, this was not publicized. Vegetarians, especially Hindus, were indeed disappointed as this information became known, as they felt the company had implied the fries were vegetarian, and the company was sued successfully in 2002. McDonald's issued an official apology and made a payment of US$five million in damages, which was distributed between a number of Hindu, Sikh, Muslim, vegetarian and academic groups.
It should be noted that in most non-U.S. or Canadian markets, McDonald's does not use any beef extract.
Another rumor circulating on the Internet claimed that a girl suffered a near death experience after eating a McFlurry. The rumor claimed that the girl was highly allergic to bird feathers. The family traced back the origins of all the food the girl had recently eaten. On phoning McDonald's head office, they were told what was in the dessert — feathers. However, this is an unsubstantiated urban legend; bird feathers are not an ingredient in its production. 
There has often been a rumor that McDonalds uses pig fat in their milkshakes or ice cream. McDonald's provides complete ingredient lists for all of its products on each of its regional websites: this includes unidentified fats within the ice cream used to make soft serve cones and sundaes.
In Australia, a rumour has floated around for years that McDonalds Apple Pies were made of chokos, not apples. This eventually led them to emphasise the fact that real apples are used in their pies.
McLibel case - A case in which McDonald's fought the distribution of a pamphlet containing multiple rumors about the corporation; while many were proven false, others were proved to be true. This, and the negative publicity given to McDonald's methods of fighting the case, made it a Pyrrhic victory for them.