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Yahoo! just replied to Facebook's counterclaims, which include the assertion of 10 (mostly acquired) patents against Yahoo!. Yahoo! asserts 2 more patents (on top of the original 10) and seeks to portray Facebook as a bad-faith litigant.

Yahoo! asserts 2 more patents against Facebook (U.S. Patent No. 7,933,903 on a "System and Method to Determine the Validity of and Interaction on a Network" and U.S. Patent No. 7,698,315 on a "System and Method Allowing Advertisers to Manage Search Listings in Pay for Placement Search System Using Grouping".

Moreover, the introductory part of Yahoo!'s filings says that Facebook asserted its patents "[i]n retaliation for Yahoo!'s good faith allegations of patent infringement", and that "Facebook lacks a good faith basis for most, if not all, of its counterclaims, particularly those patents that it purchased from others", which Yahoo! describes as non-practicing entities.

Yahoo! also claims that Facebook didn't have a good-faith basis for its infringement allegations because those assertions target "aspects of Yahoo!'s products for which there is little to no publicly-available information". Yahoo! writes: "Unless Facebook has unlawfully acquired Yahoo! confidential business information, Facebook could not have developed a good-faith basis for many of the infringement allegations in its counterclaims."

Here's what I think: Yahoo! wants to show to Facebook that escalation always goes both ways, and it tries to make Facebook's counterclaims look dubious and weak, with a view not only to the court but also the general public and existing or prospective Facebook investors. But patent transfers happen all the time, and many such patents show up in court. It's not against the law to buy patents and to assert them. Even the world's most valuable company, Apple, is suing Android device makers over patents it acquired from British Telecom and Mitsubishi, though the vast majority of Apple's patents-in-suit are homegrown ones.
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