Only two has been discovered, but how many there really is?
Actually, Theo is a mole working for the NSA and he's throughout the code that looks clean, he has hidden loads of backdoors and weak crypto…
And because the coders and security consultants reading OpenBSD's source code spend so much time laughing at the jokes in the comments, that they just don't notice the hidden evil!
But Ssh! don't tell anyone the door is opened! :-D
The alleged FBI backdoor in OpenBSD's IPSec implementation: