Link (Thanks, Marilyn!)
Inside the room was a hand-written note.
The note said "You Found It!"
It turns out, the note explained, that the house was infested with "the worst types of mold including Stachybotrys, the so-called Toxic Black Mold," which can cause "respiratory bleeding" in infants.
The stunned homeowners, thinking they might be the victims of a weird hoax, hired an environmental engineer – only to discover that the problem was even worse than they thought; the house contained "elevated levels of several types of mold, including Aspergillus, Basidiospores, Chaetomiu, Curvularia, Stachybotrys and Torula." The town's local news station calls this "the horrible secret of Number 6 Whitten Street."
Update: Sam sez, "That picture seems to be something the blogger you linked to added himself/herself. I don't think it's a real picture from the house in the story. If you look at the original story, it seems like the secret room merely had the note in it... not all that huge, obvious mold growth that's in the picture. And actually, the originally story seems to indicate the folks that left the note were really trying to help the new homeowners in the only way they could. "
Update 2: Destiny sez, "The couple will be refunded the full cost of their house by Fannie Mae -- in exchange for removing them from their (still pending) lawsuit."