A relatively minor US anti-trust case could put Microsoft back in hot water with the government, four years after settling its long-running national case.

Prosecutors in an Iowa anti-trust suit against Microsoft have been granted special permission by a judge to present evidence to the Department of Justice (DoJ) they claim proves Microsoft breached its 2002 settlement with the DoJ. That case dragged on for more than five years.

It's claimed Microsoft's engineers used at least 500 undocumented APIs to ensure Microsoft's applications worked better with Windows than those of competitors.

Software expert Ronald Alepin, who has been giving evidence on behalf of plaintiffs in Iowa, said the APIs were made available to developers outside Microsoft in a "very low profile" way in "notes form" to "discourage" developers from using the APIs, while also allowing Microsoft to claim the APIs were documented.

One stipulation of the 2002 settlement between Microsoft and the DoJ is for Microsoft to document all APIs and Windows Communications protocols for the benefit of third parties.

It's a condition Microsoft has been consistently poor at meeting. Officials regularly monitoring Microsoft's compliance under the Microsoft Communications Protocol Program (MCPP) repeatedly criticise Microsoft for its slow progress and for failing to make adequate documentation available. They've also forced Microsoft to substantially change the program, relaxing license pricing and wording.

The Iowa case, Comes v Microsoft, claims Microsoft's business practices have unfairly hurt consumers. More from the case can be found here. ®