Microsoft knowingly destroyed evidence to hinder an anti-trust investigation into it, a company suing the software giant for patent infringement has claimed.

In court documents, Burst.com accuses Microsoft managers of telling employees in 2000 to delete most or all e-mail after 30 days. At the time, the US Department of Justice was in the middle of its own anti-trust lawsuit against Microsoft. On top of that, it was also at the end of dozens of class action lawsuits.

"Given this array of litigation, Microsoft had a concrete duty to preserve relevant documents," Burst.com's lawyers wrote. "But it did not. Instead, it implemented... practices to make sure that incriminating documents disappeared."

A Microsoft spokeswoman disputed Burst.com's allegations. "Over the past several years, we have produced literally millions and millions of documents and e-mails for the various legal cases we’ve been involved in, and we’ve been completely forthcoming in all document requests in this case as well," a spokeswoman said. "We have provided more than half a million pages of documents from more than 60 employee files specifically in response to Burst’s broad discover requests."

Burst.com's motion asks the judge to instruct the jury when the case goes to trial that because Microsoft failed to retain documents relating to Burst.com's lawsuit, "the jury is free to infer that Microsoft did so because the contents of the documents were adverse to Microsoft".

Burst.com filed its lawsuit against Microsoft in June 2002, claiming Microsoft stole patented technology and trade secrets concerning Internet-based video-on-demand for its Windows Media Player product. Microsoft learned all about Burst.com's technology in two years of meetings and discussions, although it signed a non-disclosure agreement with Burst prior to those meetings, Burst.com has claimed.

Burst.com's new motion alsoasks the judge to exclude former Microsoft executive Eric Engstrom as a witness during trial. Engstrom, the former general manager of MSN's dial-up service, was a key employee in Microsoft negotiations with Intel, after which Intel ceased development of its Java Media Framework Player in 1998, according to Bruce Wecker a lawyer representing Burst.com. Burst.com's Burstware media player relied on the Intel Java framework.

With no e-mail to back up his testimony, Engstrom is "free to remember history in a way most convenient for Microsoft," Burst said. "We don't think he should be able to appear in court and make up stuff," added Burst's lawyer.

The court documents accuse Microsoft of not allowing employees to archive e-mail and claims thatJames Allchin, group vice president of Microsoft’s Platforms Group, ordered employees in January 2000 to destroy e-mail after 30 days. "This is not something you get to decide," Allchin wrote to employees, according to the Burst.com motion. "Do not archive your mail. Do not be foolish. 30 days."

But company policy is to retain e-mail relating to continuing legal actions, and Allchin's instructions on deleting unneeded e-mail is consistent with company policy, said the Burst spokeswoman.