Some 100,000 routers of type Speedport W921V, W504V and W723V are affected in Germany alone. A design flaw that exists in the WPS specification for the PIN authentication significantly reduces the time required to brute force the entire PIN. In order to exploit the backdoor, no button has to be pushed on the device itself and on some of the affected routers, the backdoor PIN (“12345670”) is still working even after WPS has been disabled by the user.
Source: https://thehackernews.com/2012/04/more-than-100000-wireless-routers-have.html