A new enemy is stalking cycling.
After many years trying to rebuild a reputation savaged by the Lance Armstrong blood doping era, the threat now comes from a form of cheating that is perhaps even more brazen.
It's known as "mechanical doping" and after many years of rumours that it exists in the sport, cycling is finally admitting it has a problem.
Less than two weeks ago Belgium's Femke Van den Driessche became the first to be banned for it. She now faces six years out of the sport.
Britain's double Tour de France winner Chris Froome believes anyone who is caught should face a life ban and their team should be penalised heavily too.
- So how does it work?
Simply explained a small, battery powered motor is hidden within a standard racing bike frame.
At the touch of a button it is activated and drives the pedals.
Potentially it can give the rider assistance on a steep climb or even an extra boost when trying to catch a group in front.
The whole mechanism is concealed from the naked eye.
Apart from taking the bike apart, there are several different ways to detect mechanical doping.
One is using infra red technology which clearly shows any "hot spots" on a bike.
So when the motor heats up the camera can easily point you to a part of the bike which is emitting an abnormally high temperature.
The camera can be used during a race but you have to get relatively close to the bike you are testing and that involves moving at some speed.
It is easy to deploy at the end of a race, but if the motor has only been used sparingly along the course it may well have cooled down before the post-race checks.
That is why the sports governing body, the UCI, favours a magnetic test which can be carried out before or after a race.
They claim this system takes less than a minute and can detect the presence of a motor, whether it's been used or not.
Whether it's fool-proof or not is impossible to judge at the moment, but there is no question the sport is taking this potential new crisis very seriously.
The director of the Tour de France believes mechanical doping is the single biggest threat to cycling at the moment and is urging those running the sport to increase dramatically the number of tests.
Cycling has barely dragged itself from its past murkiness into the light, the last thing it needs now is yet another cheating epidemic.