 In the 1970s, locksmiths in Denmark shared a technique for knocking on a lock cylinder while applying slight pressure to the back of the lock plug.When the pins would jump the inside of the cylinder, the plug would be able to slide out freely, thus enabling the locksmith to disassemble the lock quickly.The use of a bump key was not introduced until some time later and was first recognized as a potential security problem around 2002–2003 by Klaus Noch, who brought it to the attention of the German media.