Hewlett-Packard Co is suing former Chief Executive Mark Hurd following his hiring by rival technology firm Oracle Corp, court documents showed.

Oracle, the world's third-largest software maker, announced Hurd's hiring on Monday, a month after he resigned from HP over expense account irregularities related to a female contractor.

Shares of HP fell 0.6 percent to $40.10 on the New York Stock Exchange. Shares of Oracle rose 5.5 percent to $24.18.