Unified communications vendor Avistar Communications has questioned Microsoft’s motives for challenging 24 of its 29 US patents and admits any legal battle could disrupt its business.

So far, four of Microsoft’s requests have been rejected by the US Patent Trademark Office (USPTO) on procedural grounds. If all procedural flaws are corrected, the USPTO has approximately two months to decide whether or not to grant the requests and hold a full formal re-examination.

Tony Rodde, president of Avistar, said: “Avistar has a lot of questions about why Microsoft might be doing this, because some of these patents have nothing to do with Microsoft’s technology or business.”

The requests follow six months of unsuccessful discussions between the two parties about patents owned by Avistar in the fields of instant messaging, video conferencing and online collaboration.

“It is an enormous amount of patents to challenge for such a small firm. Out of the re-examinations conducted by the USPTO in 2007, Avistar made up five per cent of them. Avistar is not aware of any other company that Microsoft has done this to,” Rodde added.

If the USPTO grants the requests, the process could take between six months and two years.

Simon Moss, chief executive of Avistar, said: “Avistar is bewildered by the re-examination and we want to resolve it so everyone walks away feeling satisfied.”

In a statement, Microsoft said: “Microsoft has asked the US patent office to take another look at Avistar’s patents in light of prior art, which was not considered in the original examination of the patents. Any discussions that may be going on between the parties are confidential and we are not at liberty to discuss.”