Among the patents are several that at a glance appear to be quite broad. One of the nine patents that Microsoft alleged Salesforce.com infringed is entitled "System and method for providing and displaying a web page having an embedded menu," while another is labeled "Method and system for stacking toolbars in a computer display."

"Maybe Salesforce was betting that they're too general [for Microsoft] to defend," said Enderle. "Older patents especially are sometimes hard to defend because they're so general. We'll see."

Salesforce.com's director of public relations, Gordon Evans, declined to comment on the lawsuit today.

Microsoft had no such hesitation. "Microsoft has been a leader and innovator in the software industry for decades and continues to invest billions of dollars each year in bringing great software products and services to market," said Horacio Gutierrez, Microsoft's deputy counsel of intellectual property and licensing, in a statement.

"We have a responsibility to our customers, partners, and shareholders to safeguard that investment, and therefore cannot stand idly by when others infringe our IP rights," Gutierrez said.