Warforged are not known to the outside world. Even most Elves would have to admit they have never seen one. Only the players have encountered Warforged at this point. The party has encountered one living, sane Warforged: Crixus-3, and have fought a few living, but insane Warforged. They have also gone into an abandoned Warforged factory.
The Warforged seemed to have been created to serve as soldiers in the Old War. Not much else it known about them.