IBM is suing Joanne Olsen - a 31-year veteran of the company who used to be general manager of its services division.
Olsen was tempted away to join Oracle by Larry Ellison after the purchase of Sun Microsystems - which put the two firms in more direct competition.
Big Blue complains that Olsen was contractually obliged to take gardening leave - not work for a competing company - for at least a year.
A spokesman for IBM told Reuters: "Joanne Olsen possesses valuable confidential information about IBM and our operations. As a result, she cannot undertake a senior position at Oracle without violating her obligations to IBM."
IBM has filed against Olsen in a court in New York State. She declined to comment and Oracle spokespeople were unreachable. ®