Brazilian security forces stand guard outside the Maracana stadium in Rio de Janeiro on August 5, 2016, ahead of the opening ceremony of the Rio 2016 Olympic Games.
(Adrian Dennis/AFP/Getty Images)

Ahead of any Olympic event, there are always security concerns. The last two Summer and Winter Games took place in Britain and Russia, two countries that have been the target of terrorist plots in the past.

Brazil, by comparison, has relatively little history of terrorism. However, the 2016 Summer Games in Rio de Janeiro come at a time of heightened concern all around the world. Some worry that any complacency on the part of Brazilian authorities could present an opportunity for would-be plotters.

Is there really a link between terrorism and the Olympics? Below are five facts to help you put the situation in context.

1. There has been no consistent increase or decrease in the frequency of terrorist attacks during recent Olympics.


(Courtesy of START and the University of Maryland)

When it comes to the threat of terrorism and the Olympic Games, researchers have two conflicting hypotheses. One is that, as the Olympics are major world events, they are likely to attract would-be terrorists who hope to stage a high-profile attack. On the other hand, the increased security in host countries works to disincline terrorists and thwart plots.

Overall, it's unclear which, if either, is right.

The National Consortium for the Study of Terrorism and Responses to Terrorism (START) at the University of Maryland has put out a number of studies that looked at terrorist attacks during the Olympics and six months before the Olympics since 1972, and contrasted them with the same period the previous year.

They found that there was no clear pattern as to whether the Olympics increased or decreased the likelihood of terrorism in a host country. In part, they acknowledged that this was due to unusual events that may skew the figures — the 9/11 attacks took place the year before the 2002 Winter Olympics in Salt Lake, for example. (Please note that START's data does not include the 1994 Winter Games in Lillehammer, Norway, because of a lack of data.)

2. There have been three fatal terrorist attacks during the Olympics since 1970.

The most infamous moment of terrorism at an Olympics took place in 1972 in Munich, when eight assailants from the Palestinian Black September Organization took members of the Israeli Olympic team hostage. After a lengthy standoff and a shootout at a nearby air base, all 11 hostages were left dead, as was one West German policeman and five of the attackers.

There have since been two other terrorist attacks during Olympic Games that killed people. In 1996, a pipe bomb exploded during Atlanta's Olympic Games; it killed one person and wounded more than 100 others (a Turkish cameraman also died of a heart attack while rushing to the scene). The attacker was later identified as Eric Rudolph, who was also involved in bomb attacks on abortion clinics and gay bars.

During the 2008 Games in Beijing, a man wielding a knife killed an American businessman and wounded his wife and their tour guide. While the attack is classified as terrorism by START, the exact motives of the attacker are unknown. The perpetrator, Tang Yongming, had no known ties to terrorist organizations; he later committed suicide. A bomb also exploded in a development zone near Beijing during the games, killing two, though little is known about this incident.

3. Since 1972, there have been at least eight host cities without attacks near the Games.

Of the 22 Games studied by START, five were found to have no terrorist attacks during the Olympic Games or in the six months before it, or during the same period the year before. These locations were Japan in 1972, Canada in 1976, the Soviet Union in 1980, Yugoslavia in 1984 and Australia in 2000.

Additionally, the Olympic Games in Canada in 1988, Italy in 2006 and Canada again in 2000 had no acts of terrorism during the Games or six months before them, though they had terrorist attacks the previous year.

4. Experts consider Brazil’s risk of terrorism far lower than for other recent hosts countries.

Brazil is generally classified as a country at a very low risk of terrorism. The Global Terrorism Index, published by the New York-based Institute for Economics and Peace, last year ranked it 74th in the list of countries affected by terrorism. This places it behind most other recent host cities, including Russia (23), Britain (28), Canada (72), China (22), Italy (54), Greece (29), the United States (35) and Australia (59).

START's data for Brazil show five terrorist attacks in the country during all of 2015. These attacks killed a total of three people and left no other wounded, according to the data. In all three of these fatal attacks, journalists who focused on corruption were the victims.

Brazil, where the Muslim population is less than 1 percent of the population, has relatively little history of terrorism inspired by Islamic extremist groups. However, two weeks before the Olympic Games were scheduled to begin, police arrested 12 people who the government claimed were an "amateur" cell inspired by the Islamic State. Brazil's security services are on high alert during the Games, with at least 80,000 security personnel working in Rio during the Games — double the number deployed in London in 2012.

5. The deadliest mass killing linked to a modern Olympic Games wasn’t terrorism.

While plenty of attention is rightfully placed on terror risks at Olympic Games, the worst moment of mass violence linked to the modern Olympic Games didn't come from a terror group. Instead it came from the army.

Ten days before the 1968 Summer Olympics in Mexico City were due to start, activists had assembled in the city's Tlatelolco to protest the country's authoritarian government, which was deeply concerned about its international image ahead of the Games. In the end, as many as 300 people are thought to have been killed when the army opened fire on protesters. The event is now remembered as one of the bloodiest and most controversial incidents of Mexico's "dirty war."

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