The battle between Apple and VirnetX  has been ongoing for over a decade. We began covering this serious patent infringement case in 2012 and have covered it in various reports since (01, 02 and 03). Today, VirnetX has lost a key dispute with Apple sending their stock down 13%.

Reuters is reporting that Apple Inc convinced a U.S. appeals court on Thursday to uphold a patent tribunal's ruling that could imperil a $502 million verdict for patent licensing company VirnetX Inc in the companies' long-running fight over privacy-software technology.

The U.S. Court of Appeals for the Federal Circuit affirmed a decision from the U.S. Patent and Trademark Office that invalidated the two patents VirnetX had accused Apple of infringing.

Apple has separately appealed the verdict itself, but the Federal Circuit has yet to rule in that case. The court heard combined arguments in both cases in September, and both sides said upholding the decision to cancel the patents would also likely negate the jury award.

"If the court upholds the [USPTO's] decision, we have a big problem," VirnetX attorney Jeff Lamken of MoloLamken said at the September hearing. "I don't think we have an enforceable judgment."

The Federal Circuit on Thursday affirmed decisions by the USPTO's Patent Trial and Appeal Board that the patents were invalid in light of earlier publications that described the same inventions. For more, read the full Reuters report.