Hurd was HP's CEO for five years and his former company does not want him anywhere near rival Oracle, much less serving as co-president.
HP claims an executive job at Oracle would violate Hurd's two-year separation and confidentiality agreement.
"They are concerned that clearly, about the competitive threat that he poses, particularly about the ways in which Hurd might be able to help Sun Microsystems, now part of Oracle, compete more effectively with Hewlett Packard," Santa Clara University law professor Eric Goldman said.
The lawsuit says, "Hurd will be in a situation in which he cannot perform his duties for Oracle without necessarily using and disclosing HP's trade secrets and confidential information to others."
Chuck House worked for HP for 30 years and wrote the book published last year called "The HP Phenomenon." He says Oracle CEO Larry Ellison knew he was picking a fight with HP and did not care.
"I think Larry knew full well what he is doing, there's no question he knew this would ring the bell over at the HP board and in the HP executive suite," House said.
Late Tuesday, Oracle sounded offended, calling the HP lawsuit "vindictive."
In a statement Oracle said, "The HP board is making it virtually impossible for Oracle and HP to continue to cooperate and work together in the IT marketplace."
Despite Hurd's signature on multiple confidentiality agreements, Goldman says this is not a slam dunk for HP.
"California courts are very reluctant to restrict employment and it's not entirely clear to me if they would agree with HP's assessment of the situation," he said.
Oracle shares were up more than $1.30 on the day following Oracle's announcement of Hurd's hiring.