The first top-level case of "technological fraud" came to light after a bike was seized at the Cyclo-cross World Championships on Saturday.Belgium's Femke van den Driessche, who was riding it, said she knew nothing about the device and that the bike belonged to someone else.But the International Cycling Union is investigating and the bike manufacturer is threatening legal action against Van den Driessche.Why is it such a big deal?Cycling has a long history of cheating, with those seeking to gain an illegal advantage traditionally using drugs.There are numerous examples of blood dopers, the most notorious of them being Lance Armstrong.The American was stripped of his seven Tour de France titles after being accused of the "most sophisticated, professionalised and successful doping programme sport has ever seen".Now, just when it seemed cycling was getting clean, a new threat emerged: doped cycles.How much of a problem is it?Nothing has been proven yet but there have been plenty of rumours, not to mention allegations, against some of the world's top riders.Swiss rider Fabian Cancellara was accused of "mechanical doping" in 2010 when an Italian film released on YouTube claimed to show the Olympic time-trial champion using a battery-powered motor.In 2014, the UCI investigated allegations that Canada's Ryder Hesjedal used a motorised bike after video footage seemed to show the rider's wheel moving by itself following a crash at the Vuelta a Espana.Cancellara and Hesjedal rejected the allegations as "stupid" or "ridiculous".Former Tour de France champion Alberto Contador has also been forced to deny allegations of using a motor-powered bike.How do 'doped bikes' work?Motorised bikes are available to the public and designed to encourage people to take up cycling, although it is really expensive to buy a basic model.Riders still have to pedal but they can also get assistance from a battery-powered engine."You have to cycle and then you push a button," says Harry Gibbings, chief executive of Typhoon, which builds the bikes."The silent motor is engaged and, to the rider, it's like someone is giving them a push."The motor can produce up to 250 watts of power and gives motorised assistance up to a speed of 25km an hour.Is that a big deal?Former British Olympic cyclist Rob Hayles believes the advantage of a motorised bike is huge, especially on hill climbs."If you are averaging, say, 350 watts for a 200km race and can generate an extra 50 watts, that is a big percentage," he says."It's a bigger advantage than doping with which your body still has to do the work."How are motors detected?A report in cyclo-cross magazine Grit.cx said UCI officials were seen using a tablet-like device to check for mechanisms inside the frame of Van den Driessche's bike.Apparently, the device used electromagnetic-based technology to detect the secret motor. Once officials decided closer inspection was needed, they removed the saddle post to find wires poking out. ..