A US Federal Court has confirmed that ‘Trojan Horse’ claim corrections are not permissible before the United States Patent and Trademark Office.

Most patent jurisdictions have a mechanism by which a patent proprietor can, after grant of a patent, correct any errors within the patent. In order to provide legal certainty to third parties, corrections are quite limited in scope so as to not broaden the scope of protection afforded by the patent and are examined by the relevant authority to ensure that this is the case.

In the US, the mechanism by which a granted claim can be corrected is known as ‘reissue’, where the proprietor seeks the issuance of a correct patent. A patent proprietor can seek a ‘broadening reissue’, i.e. where the reissued patent is broader than the originally granted patent, provided that the reissue is sought within 2 years of grant, and the request meets the standard required to allow a correction. One of the main criteria for a broadening request to be allowed is that it cannot ‘re-capture’ subject matter intentionally surrendered in prosecution.

A ‘Trojan Horse’ correction is where an applicant seeks reissue of a granted US patent to allegedly ‘correct’ a claim, whilst in fact the correction is sought in order to recover claim scope lost in prosecution.

In this case, the applicant had previously surrendered part of their original claim scope, in order to overcome the USPTO’s objections that said claim scope was obvious. Specifically, the applicant (in response to a USPTO objection) required that the independent claims include a processor.

However, once the application was granted (with this claim scope removed), the applicant sought to ‘correct’ the granted claims, and in doing so remove the claimed processor, and reinstate the original claim scope.

The request for reissuance stated that there was an error within the claims, in that this limitation was ‘unnecessary’, and as such the proprietor therefore sought removal of this limitation.

Whilst the request for reissue was filed within the two year period for seeking ‘broadening reissue’, the request was rejected by the examiner in view of the fact that there was no error in the claims which could validly be corrected by a reissue, and that the request was merely attempting to re-capture subject matter intentionally surrendered in prosecution. This ‘re-capture’ of previously surrendered subject matter has long been prohibited by the USPTO.

The proprietor, following a denial of a request for a hearing, appealed the rejection to the Court of Appeals for the Federal Circuit.

The Court agreed with the original decision to reject the request for reissue, as it was determined that the original limitation was not an error in the granted patents and was instead made deliberately by the applicant in order to overcome the USPTO objection.

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