Magistrate Brooke Wells dismissed 182 of SCO's 294 claims, dealing a major setback to SCO's $5 billion lawsuit.
The suit, filed in 2003, accused IBM of donating SCO's Unix code to Linux developers, but Wells ruled SCO had produced virtually no proof of the allegation.
She said SCO had "willfully failed to comply" with court orders to show IBM which of millions of lines of code in Linux were supposedly misappropriated. SCO argued that was IBM's job.
Wells likened SCO's stance to a security guard who accuses a shopper of stealing merchandise -- and demands the shopper show proof of the theft.
"It would be absurd for an officer to tell the accused that 'you know what you stole; I'm not telling,'" Wells wrote in a 39-page decision signed Wednesday.