Facebook sued over 'like' button
Facebook is facing legal action over its use of the "like" button and other features of the social network.
It is being sued by a patent-holding company acting on behalf of a dead Dutch programmer called Joannes Jozef Everardus van Der Meer.
Rembrandt Social Media said Facebook's success was based, in part, on using two of Mr Van Der Meer's patents without permission.
Facebook said it had no comment to make on the lawsuit or its claims.
A lawsuit has been filed in a federal court in Virginia by Rembrandt Social Media.
"We believe Rembrandt's patents represent an important foundation of social media as we know it, and we expect a judge and jury to reach the same conclusion based on the evidence," said lawyer Tom Melsheimer from legal firm Fish and Richardson, which represents the patent holder.
Rembrandt now owns patents for technologies Mr Van Der Meer used to build a fledgling social network, called Surfbook, before his death in 2004.
Mr Van Der Meer was granted the patents in 1998, five years before Facebook first appeared.
Surfbook was a social diary that let people share information with friends and family and approve some data using a "like" button, according to legal papers filed by Fish and Richardson.
The papers also say Facebook is aware of the patents as it has cited them in its own applications to patent some social networking technologies.
Also cited in the same legal claim was another social media company called Add This.