In an email sent to the New York Times and later provided to Reuters by Oracle, Ellison slammed HP's board for ousting Hurd -- a close friend -- even after the PC maker's board determined Hurd had not violated its sexual harassment policy.
HP disputed Ellison's account of events.
Hurd resigned on Friday after a probe into sexual harassment allegations turned up expense account abuses that HP said were intended to cover up his relationship with a female contractor.
The HP board just made the worst personnel decision since the idiots on the Apple
In losing Mark Hurd, the HP board failed to act in the best interest of HP's employees, shareholders, customers and partners, he said.
Ellison said the HP board voted 6-to-4 to go public with the sexual harassment claim against Hurd.
Publishing known false sexual harassment claims is not good corporate governance; it's cowardly corporate political correctness.
The Oracle chieftain did not say in his email how he came about his information.
An HP spokeswoman said: As the company stated previously, the board voted unanimously for Mr. Hurd's resignation. And, that was the only vote the board took on this issue.
According to Ellison, HP directors debated whether the company needed to disclose Jodie Fisher's sexual harassment claim against Hurd. Fisher has said she did not have an intimate sexual relationship with Hurd. The two have settled the claim privately.
Oracle, the world's third-largest software maker, is a major partner of HP, the No. 1 PC maker. Oracle now also competes with HP in the server market, following its purchase of Sun Microsystems.
Ellison said the company's charge that Hurd engaged in expense fraud was not credible.
What the expense fraud claims do reveal is an HP board desperately grasping at straws in trying to publicly explain the unexplainable, Ellison wrote.
Shares of Palo Alto, California-based HP closed down 8 percent at $42.60 on Monday.
(Editing by Edwin Chan, Gary Hill)