By now you've heard that Yahoo has sued Facebook, alleging patent infringement. But just which pieces of intellectual property is Yahoo claiming Facebook ripped off?

Surely, you'd say, Yahoo doesn't claim that it invented the entire social networking model Facebook is based upon—except it turns out that is almost exactly what Yahoo is claiming.

"Facebook's entire social network model, which allows users to create profiles for and connect with, among other things, persons and businesses, is based on Yahoo!'s patented social networking technology," Yahoo claims in the lawsuit, filed yesterday in US District Court in Northern California. "Prior to adopting Yahoo!'s patented social networking technology in 2008, Facebook was considered one of the worst performing Internet sites for advertising. Facebook's use of that social networking model has reportedly dramatically driven up Facebook's advertising click through rates."

Nearly all the technology that makes Facebook successful is based on Yahoo patents, the company further states.

"For much of the technology upon which Facebook is based, Yahoo! got there first and was therefore granted patents by the United States Patent Office to protect those innovations. Yahoo!'s patents relate to cutting edge innovations in online products, including in messaging, news feed generation, social commenting, advertising display, preventing click fraud, and privacy controls," Yahoo alleged in its court filing. "These innovations dramatically improve user experience, privacy, and security and enhance the ability of advertisers to connect with users."

What does Yahoo want? Money. Lots of money.

"Even if Facebook were to subsequently pay past due royalties, it would still enjoy a market share it has developed during its period of 'free riding' on Yahoo!'s intellectual property. Yahoo! would likewise lose its portion of the market share for this period. Due to the difficulty in predicting whether, if at all, such market share can be recovered, Yahoo!'s harm cannot be compensated by payment of past due royalties alone."

Yahoo doesn't specify a dollar amount. But whatever amount of damages the court sees fit to grant, Yahoo says those damages should be tripled "in view of the willful and deliberate nature of the infringement."

Yahoo is asserting ten patents against Facebook, divided into five categories: social networking, advertising, privacy, customization, and messaging. Facebook, by the way, apparently owns just 21 US patents, while Yahoo has more than 1,000.

Yahoo notified Facebook of the allegedly infringed patents on Feb. 27, and then filed suit after Facebook apparently refused to pay the licensing fees Yahoo demanded. Let's take a look at each of the ten patents being asserted against Facebook, organized by the category divisions used in Yahoo's lawsuit.

Yahoo's social networking patent

Patent #7,747,648: "World modeling using a relationship network with communication channels to entities"

Yahoo asserts just one patent in what it calls the social networking category (although all ten patents relate to social networking in some way). Filed in 2005 and issued in 2010, the patent describes "A method, apparatus, and system directed towards managing a view of a social network user's personal information based, in part, on user-defined criteria." That sounds a lot like Facebook's news feed and user walls, although Yahoo claims the patent is specifically violated by Facebook Pages and Groups. The patent goes on to say, "The user-defined criteria may include degrees of separation between members of the social network, a relationship to the prospective viewer, as well as criteria based, in part, on activities, such as dating, employment, hobbies, and the like."

According to the patent claim, Yahoo's technology includes a "world model data store" configured to store all the different, inter-related categories of people, businesses, places, "tangible things," communities, thoughts, and events that might appear on a social network. It also includes ways of organizing, searching, and displaying the data.

Yahoo's privacy patents

Patent #7,269,590: "Method and system for customizing views of information associated with a social network user"

Filed in 2004 and issued in 2007, Yahoo alleges this patent is violated by Facebook's privacy controls. The patent doesn't specifically mention privacy, but covers the view a user is given of another social network user's personal information based on "user-defined criteria" such as degrees of separation between network members and aspects like "dating, employment, hobbies, and the like."

Patent #7,599,935: "Control for enabling a user to preview display of selected content based on another user's authorization level"

Filed in 2005 and granted in 2009, this patent is also infringed by Facebook's privacy controls according to Yahoo. The technology described is similar to Facebook's "view as" feature, which lets you see what your profile looks like to other members of the site. The Facebook feature is useful for determining how tweaking privacy settings affects the amount of information friends and site users can access on your profile.

The Yahoo patent covers a system for "Enabling a first user to preview content as it would be seen by a second user, if the second user had a selected user relationship with the first user." The preview display shows "the portions of content that would be accessible to other users assigned the same user relationship or assigned a closer user relationship." The Yahoo patent claim goes on to describe the interaction between a client device and server necessary to perform the patented action.

Yahoo's messaging patent

Patent #7,406,501: "System and method for instant messaging using an e-mail protocol"

Filed in 2003 and issued in 2008, this patent covers a system for letting instant messaging users exchange messages with e-mail users. Yahoo claims it is infringed by Facebook Messages, which Facebook says offers "texts, chat and email together in one simple conversation."

Yahoo's patent describes a system in which "To the instant messaging user, the experience is a seamless exchange of instant messages; to the e-mail user, the experience is a seamless exchange of e-mail messages. Conversion of an instant message to an e-mail message includes insertion of a token into the e-mail message, and conversion of an e-mail message to an instant message includes validating a token extracted from the e-mail message."

Yahoo advertising patents

Patent #7,668,861: "System and method to determine the validity of an interaction on a network"

Filed in 2007 and issued in 2010, this patent covers a way of classifying user interactions on a network, collecting data about the interaction and then generating a "value score" to rate user interactions and sort them into different classifications. These interactions include clicking on advertiser links, with the patent also covering a method of telling the advertiser which classification the user interaction falls into. This is all related to determining the correct amount advertisers should be billed.

The patent notes that some users block cookies, meaning website operators need a more accurate method of determining the number of unique visitors, or risk losing advertising revenue. When advertising fees are based on click-through rates, it's also necessary to identify clicks that aren't legitimate.

"A malicious user easily could generate interactions on the operator's website which would create charges for advertisers (buyers of the pay for placement and performance space) when such a user has no interest in the advertiser's products or services," the Yahoo patent states.

Yahoo claims broadly that the Facebook Ads service violates the patent.

Patent #6,907,566, #7,100,111, and #7,373,599: "Method and system for optimum placement of advertisements on a webpage"

We're lumping these three patents together because they all have the same title, and were assigned to Overture Services, which was acquired by Yahoo in 2003. Filed between 1999 and 2003, and issued between 2005 and 2008, these are all infringed by Facebook Ads, Yahoo claims.

The '566 patent covers a system for placing graphical advertisements on a webpage in a way that increases the likelihood that specific users will click on them. The system learns user preferences over time and displays ads accordingly. "Data regarding the past performance of the objects is stored and updated as new data is received," the patent sates. "A user requests a page from a server associated with system. The server uses the performance data to derive a prioritized arrangement of the objects on the page. The server performs a calculation regarding the likelihood that an event will occur for a given object, as displayed to a particular user. The objects are arranged according to this calculation and returned to the user on the requested page."

The '111 and '599 patents both describe a similar method and system as covered in '566.

Yahoo's customization patents

Patent #7,454,509: "Online playback system with community bias"

The customization patents cover methods of "creating custom data streams and web pages for users based on community and user preferences," and are both violated by Facebook's News Feed and Wall, Yahoo claims. The '509 patent, filed in 2001 and issued in 2008, covers the creation of a music playback system or "other data streams" by analyzing overlap among user preferences. "Information derived from user accounts form the basis of a community and collateral preferences allow other subscribing individuals to enjoy the benefit of wider-ranging tastes according to the preferences expressed by the other members of the community," the patent states.

Patent #5,983,227: "Dynamic page generator"

Filed in 1997 and issued in 1999, this patent covers a technology for dynamically generating webpages based upon the user's preferences. While the patented claim is broad, it seems to have been intended to cover the custom news pages common to many websites, rather than the social networking technology used by Facebook. The patent also describes a method of storing data that speeds up the process of displaying webpages.

"Typically, the pages served are news pages, giving the user a custom selection of stock quotes, news headlines, sports scores, weather, and the like," the patent sates. "With the live data stored in a local, shared memory, any custom page can be built within the page server, eliminating the need to make requests from other servers for portions of the live data. While the shared memory might include RAM (random access memory) and disk storage, in many computer systems, it is faster to store all the live data in RAM."

What's next

Facebook promises to defend itself against the lawsuit, saying in a statement to Ars and other media outlets that "We’re disappointed that Yahoo, a longtime business partner of Facebook and a company that has substantially benefited from its association with Facebook, has decided to resort to litigation. Once again, we learned of Yahoo’s decision simultaneously with the media. We will defend ourselves vigorously against these puzzling actions."

Patent disputes often come down to which company has the most patents. If Facebook's patent portfolio were as strong as Yahoo's, a cross-licensing deal ending litigation would be more likely. Matt Rosoff at Business Insider speculates that Microsoft—which has a giant patent portfolio and a financial stake in Facebook—should help its partner out of this jam.

Facebook doesn't have many patents, as mentioned earlier, but some of them seem to cover functionality Yahoo claims is stolen. For example, Facebook has patents on "dynamically providing a news feed about a user of a social network," "generating a feed of stories personalized for members of a social network," and "managing information about relationships in a social network via a social timeline."

Yahoo said in a statement to Ars that it is confident it will win the suit. “Yahoo! has invested substantial resources in research and development through the years, which has resulted in numerous patented inventions of technology that other companies have licensed," the company said. "These technologies are the foundation of our business that engages over 700 million monthly unique visitors and represent the spirit of innovation upon which Yahoo! is built. Unfortunately, the matter with Facebook remains unresolved and we are compelled to seek redress in federal court. We are confident that we will prevail.”