Microsoft will mount a fresh legal challenge to the Eolas patent after being given the go-ahead to do so.
The US Patent and Trademark Office (USPTO) will hear Microsoft's argument that it invented the software technology described by patent, not the University of California and researcher Michael Doyle and their jointly-owned company, Eolas.
The patent describes a method for embedding and displaying content within web pages. In 2003 a jury ordered Microsoft to pay $521m (260m) for infringing the patent. The USPTO has revisited Eolas' claim and found in its favour.
Microsoft claims that it invented the technology before the Eolas registered its patent. If it can prove "prior art" then it is likely that the patent will either be scrapped or handed to Microsoft.
Even if Microsoft does not overturn Eolas' claim, a recent ruling by the US Supreme Court that US patents do not apply internationally is likely to result in a much reduced infringement payment.
