Salesforce.com Inc is suing Microsoft Corp for alleged patent violations, the latest development in a legal battle that began last month when Microsoft accused Salesforce of stealing its intellectual property.

The world's biggest maker of Web-based software charged that Microsoft is infringing five Salesforce patents in programs, including in the Windows Server operating system and the widely used .Net platform.

Microsoft's continuing acts of infringement have caused and are causing irreparable harm to Salesforce.com, the complaint said.

Salesforce is seeking unspecified damages in the suit, which was filed in U.S. District Court for the District of Delaware on Thursday.

The battle began on May 18 when Microsoft sued Salesforce in federal court in Seattle, alleging its rival uses its technology in software menus, toolbars and graphical interface features.

Microsoft Deputy Chief Counsel Horacio Gutierrez said in a statement that his company is now reviewing the lawsuit.

We remain confident in our position and will continue to press ahead with the complaint we initiated in the U.S. District Court for the Western District of Washington, he said.

The case is: Salesforce.com Inc v Microsoft Corp, case number 1:10-cv-00555, in the U.S. District Court for the District of Delaware.

(Reporting by Jim Finkle; editing by Andre Grenon)

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