Microsoft has mounted an indirect legal attack on Google over its highly successful Android smartphone operating system, accusing handset maker Motorola of patent infringement for including the software in its own devices.

The action adds to a growing pile of lawsuits over Android that has been filed by some of the tech industry’s leading names in recent months.

However, the legal challenges have not slowed the momentum of the software platform, which overtook Apple’s iPhone software in the second quarter of this year in worldwide shipments, according to research group Gartner.

Earlier this year, Apple sued HTC, the Taiwanese handset maker, alleging patent infringement in its Android phones, while Oracle attacked Google last month, claiming Android illegally included elements of its Java software.

On Friday, Microsoft filed claims with the US International Trade Court and in a Federal court in Seattle, accusing Motorola’s Android handsets of infringing nine of its patents. The claims cover some of the most basic functions on smartphones, including the way they synchronise with e-mail held on servers, as well as with calendar and contacts information.

While the suit targets Motorola, “the patented features implicated in the action are in the Android platform” itself rather than in technology added by the handset maker, said Horacio Gutierrez, Microsoft’s deputy general counsel.

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