Research in Motion (RIM) has countersued Visto, the wireless email specialist that formally accused it of intellectual-property infringement on Monday. RIM's complaint demands the Dallas court declare its products do not incorporate technology detailed in Visto's patents.

RIM is alleged to have infringed Visto patents 6,023,708, 6,085,192, 6,151,606 and 6,708,221. The company said it believes Visto's patents are invalid and denied infringement in any case.

Visto filed its complaint against RIM on Monday having successfully prosecuted another wireless email company, Seven Networks, the previous Friday for infringement of many of the same patents. Visto also has comparable lawsuits in motion against Microsoft, Good Technology, Smartner and Sproqit.

RIM has only just settled its long-running battle with NTP - which owns a stake in Visto, acquired in December 2005 and accompanied by the provision of Visto with a licence for NTP's technology. RIM agreed to pay NTP $613m for access to the latter's technology, even though NTP's patents may yet be declared invalid by the US Patent and Trademark Office following a number of re-appraisals of their claims. ®