A lawsuit filed by Implicit Networks alleges Microsoft Windows Vista, Windows 7, and Windows Server 2008 are violating its patent rights.

Implicit claims its patent, US 6,629,163 and with the wordy title Method and System for Demultiplexing a First Sequence of Packet Components to Identify Specific Components Wherein Subsequent Components are Processed without Re-Identifying Components is used in Microsoft's Windows Filtering Platform.

Source: TG Daily
That said, this is not the first time Implicit Networks has claimed patent infringement against a tech industry heavyweight. Past allegations have been directed towards AMD, Intel, Sun Micro, and more.