Vertical Computer is suing Microsoft claiming that its .Net framework violates patents it holds.
Patent number 6,826,744, describes "a system and method for generating computer applications in an arbitrary object framework" belongs to Vertical. The company says that it "separates content, form, and function of the computer application so that each may be accessed or modified separately".
Vertical issued a cease and desist notice in February and surprisingly Microsoft continued to sell products based around .Net.
Both Microsoft's .Net and Vertical Computer's patented SiteFlash product create component-based programs in XML which are used to build and control websites.
If Vertical wins then Microsoft will have to make significant changes to its .Net Framework.