Oracle's chairman and chief executive officer has defended his company's decision to hire a detective firm to investigate three advocacy groups that have acted favourably towards Microsoft. At the same time, the Oracle chief sought to play down his personal involvement in the investigation, at first denying any knowledge of it.

"We've gathered enough evidence to indicate these are not independent groups as they pretend to be," Larry Ellison said, speaking at a press conference at the company's headquarters here. "We got evidence -- we proved -- that these organisations were paid for by Microsoft's public affairs and legal departments."

Reports have recently surfaced that Oracle had hired the Washington, DC detective firm Investigation Group International (IGI) to monitor the activities of three advocacy groups -- the Independent Institute, the National Taxpayers Union, and the Association for Competitive Technology (ACT). Oracle accused the groups of masquerading as "independent advocacy groups" when they are in fact funded largely by Microsoft.

Answering questions from reporters, Ellison at first denied all knowledge of IGI's investigation, which he said was launched a year ago at the behest of Oracle's legal affairs group in Washington. The first he knew of the investigation, he said, was when he read reports about it in Tuesday's New York Times.

"I never knew anybody was going through people's garbage. I don't approve of going through people's garbage," Ellison said. "I had never heard of IGI until yesterday. I never knew we were doing any of this stuff."

According to the Times article, IGI tried to bribe the cleaning staff in at least one of the organisations to turn over the contents of trash bins.

When pressed by reporters here, Ellison acknowledged being aware that the investigation was underway, but said that he didn't know what methods were being employed, or who was conducting it.

"Did I know we were investigating Microsoft's covert efforts to unduly influence public opinion? Absolutely," Ellison said. "Do I take full responsibility? Yes, absolutely. It happened on my watch. I authorised the funding."

Some pundits are already referring to the affair as "Larrygate", after the Watergate scandal that eventually toppled the administration of US president Richard Nixon in the early 1970s.

The investigation of Microsoft was justified because it exposed the software giant's "covert" funding for public advocacy groups in an effort to sway public opinion during Microsoft's antitrust trial, Ellison said. In a series of animated responses to reporters' questions, he slammed the advocacy groups as being Microsoft puppets working on the software maker's behalf.

"The Independent Institute is neither independent nor an institute," Ellison quipped. The Association for Competitive Technology is "supposed to be supporting all Americans. In fact, it supports just two Americans, (Microsoft's) Bill Gates and Steve Ballmer, and it was our intention to expose that."

The three groups involved have vehemently denied any wrongdoing. In a statement issued on Tuesday, the Independent Institute professed disappointment at what it called Oracle's attempt to "smear us by calling into question the legitimacy of our 14-year scholarly, public-policy research program".

"Instead of being willing to address the issues openly, Oracle has apparently felt the need to employ back-alley tactics, subterfuge, and disinformation in order to achieve its aims," David Theroux, founder of the Independent Institute, said in the statement.

Microsoft also responded to Ellison's comments.

"The only thing more disturbing than Oracle's behaviour is their ongoing attempt to justify these actions," the Microsoft statement said. "Mr. Ellison now appears to acknowledge that he was personally aware of and personally authorised the broad overall strategy of a covert operation against a variety of trade associations.

"This is dramatic evidence that Microsoft's competitors have engaged in a massive and ongoing campaign to unfairly tarnish Microsoft's public image and promote government intervention to benefit themselves," Microsoft said in the statement.

Ellison sought to maintain the moral high ground.

"I feel very good about telling you about what we did," he said. "Maybe our investigating organisation did some things that were unsavoury -- certainly from a personal hygiene point of view. But we got the truth. I believe in full disclosure."

He challenged Microsoft to launch a similar investigation of Oracle.

"We'll ship them our garbage," Ellison said, with obvious relish. "We will send all of our garbage to Redmond and they can go through it."