A key patent that Apple successfully used against Samsung in its multibillion-dollar courtroom brawl earlier this year is at risk following a re-examination by the U.S. Patent and Trademark Office.

All 21 claims of U.S. patent No. 7,844,915 -- also known as the "pinch to zoom" patent -- were rejected by the Patent Office today, following a re-examination.

Samsung pointed this out in a filing to U.S. District Court Judge Lucy Koh this afternoon, noting that it was "relevant" given the company's effort for a retrial, as well as Apple's attempt at an injunction against a number of Samsung devices for infringing on this very patent. Both of those efforts were shot down in court orders earlier this week.

Apple has an opportunity to combat the decision as part of the proceedings.

The '915 patent covers technology that can distinguish whether a user is scrolling with one finger versus using several touch points at once for a pinch-to-zoom action. A California jury said that 21 of the 24 accused devices sold by Samsung Electronics infringed on the main claim of that patent.

That patent played a role in assigning the damages at the end of the case, which totaled just over a billion dollars. That figure is still subject to change pending some follow-up orders by Koh, which are expected soon.

In the Patent Office's re-examination decision, the organization said all 21 claims of the patent were invalid based on claims from other patents, including one from the U.S. and one from Japan.

Samsung and Apple both declined to comment further beyond the filing.

The decision comes weeks after the Patent Office tentatively invalidatedanother Apple software patent covering the rubber-banding effect found on iOS. Like the pinch-to-zoom patent, it too was used successfully against Samsung as part of the same lawsuit. Unrelated, but more recent, was another Apple patent covering touch-screen technology, which wasdeemed invalid by the Patent Office.

Corrected at 3 p.m. PT to note that the patent is under reexamination, giving Apple a chance to fight the decision, and to adjust the number of claims covered. Updated again at 4:34 p.m. PT to note that Apple declined to comment.