Facebook is getting sued yet again it seems, this time for patent infringement, writes Web 2.0-watcher Michael Arrington on TechCrunch .

The lawsuit apparently refers to a violation of US Patent 6,519,629 , which was approved in February 2003.

What is Facebook doing wrong?

The patent claims ownership of an "Information and Application Distribution System" designed to "allow interaction and communication within like-minded communities".

Go deeper and the patent specifically mentions: "the transmission and receipt of an "invitation application" which contains both a message component and an executable component to enable multiple users to connect within a specific community."

It also goes on (at considerable length) to claim for "a system for creating a community for users with common interests to interact in".

On the surface, portions of the patent do sound similar to some Facebook mechanisms. On Facebook you send 'invitations' to other registered users in order to become 'friends' with them. You can also create community focused 'groups' for like-minded users, adjust the privacy levels of these groups and so on.

But the descriptions in the patent also sound like typical forum elements (discussion threads, topics, etc), albeit dressed up with fancier names and incorporating significantly improved customisation options.

A $6 billion Facebook is an obvious target

Beyond community creation, there's a lot of detail in the patent that Facebook doesn't seem to infringe. Yet there are also references to "optional applications", which will undoubtedly be linked to Facebook's popular 3rd party mini-apps, such as iLike, Poke Pro and TravBuddy.com.

With Facebook recently valued at $6 billion, it's hardly surprising that founder Mark Zuckerberg finds himself saddled with another lawsuit.

The in-vogue social networking site is already being taken to court by the owners of rival friend-to-friend site ConnectU . They maintain that Zuckerberg stole code and ideas from them when they worked together at Harvard University.