The US Patent Office has struck down two more patents held by the IP company NTP, which has been a costly thorn in the side of Research in Motion. Seven out of eight patents that formed the core of NTP's litigation have now been invalidated.

A settlement formed in March this year saw RIM agree to pay $450m to license the patents. But RIM says NTP is refusing to honor its side of the deal, and reports have surfaced hinting that NTP wanted better terms than the two parties had agreed. RIM has asked a Virginia District Court to enforce the deal.

Donald Stout, co-founder of NTP, told CNET this week that the patents were worth over a billion. Nokia has struck a licensing deal with NTP for an undisclosed sum. ®

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