In terms of terrorism, sport long ago lost its innocence. The 1972 Munich Olympics, at which 11 Israeli athletes and coaches were killed by the Black September group, illustrated there is no more fertile arena for drawing attention to a cause.
Nor, sometimes, is there a softer target. A huge security effort is needed to safeguard the large number of people gathered for a major sporting occasion. The potential for a terrorist attack multiplies when the event takes place not within the restricted space of a stadium but on the streets of a large city - a city, for example, like Boston and an event like a marathon that attracts thousands of runners from all over the world and hundreds of thousands of spectators.
Because the threat is so obvious, it is perhaps surprising there have been no other bombings like the one that this week killed three people and injured more than 170 near the Boston Marathon finish line.
One reason for this is the reinforced security in force in the United States since the aerial assault on the World Trade Centre in September 2001.
Another is worldwide recognition of the vulnerability of sporting events. The $1.6 billion security operation at last year's London Olympics included thousands of police and troops, surveillance aircraft, sniper-carrying helicopters and missile batteries on rooftops.
London, like the post-2001 Olympics at Salt Lake City, Athens, Turin, Beijing and Vancouver, escaped unscathed. Paradoxically, the deadly attack on the Boston Marathon means that big sporting occasions in the immediate future will also almost certainly be trouble-free. Airline travel became safer after 9/11 because of the much stricter airport security, especially that administered by the Transportation Security Administration in the US.
Heightened security will also be the order of the day at the likes of next year's Winter Olympics at Sochi, Russia, soccer's World Cup in Brazil, and the 2016 summer Olympics in Rio de Janeiro. As much has been confirmed by International Olympic Committee senior member Gerhard Heiberg, who said after the Boston bombings that "security is priority number one, no question about it".
Even marathons, such as that on the streets of London this weekend, are more likely to pass without incident. Access to areas such as the finish line is certain to be stricter than that applied in Boston.
Yet that does not mean the world is now a safer place. Terrorists, whether organisations or deranged individuals, will be encouraged by the publicity generated by the carnage in Boston. They will also recognise that occasions like the Sochi Olympics, at which an event like cross-country skiing presents obvious security difficulties, are probably now too difficult a prospect, at least in the short term. They like to give the impression they can strike anywhere, but that is far from the case. Their own weakness and their very mode of operation mean they have a severely limited number of prospective targets.
They can expect little success if they try to breach closely guarded embassies or government offices, for example. They must select targets where the mood is relaxed, attack is not expected, and security is difficult to enforce. Targets like bars in Bali crowded with young Western tourists, or a world-famous race through the streets of Boston.