Two months ago, Xerox sued Google and Yahoo for patent infringement, and the two defendants haven’t responded by pulling out their checkbooks.  They’ve instead taken the interesting (though not unexpected) step of making counterclaims.

Apparently Google and Yahoo are willing to accept either of a couple explanations for why they’re not guilty of infringement.  Reuters reported, "In filings in Delaware federal court on Thursday, the defendants sought declarations that they did not infringe the two patents at issue, or variantly that the patents are invalid and thus cannot be enforced by Xerox."

That’s a rather interesting approach, but one that’s hard to argue with.  It’ll allow Google and Yahoo’s lawyers to look for loopholes even as they claim that the patents are too broad (one covers generating queries based on keyword searches, while the other relates to updating pages based on user reviews).

Also, even if the tactic seems a little unrefined, a whole lot of products – including AdSense, AdWords, Google Maps, Google Video, YouTube, the Yahoo Publisher Network, Yahoo Search Marketing, Yahoo Shopping, and the Y!Q Contextual Search tool – might be affected by the outcome of this case, so it’s natural that Google and Yahoo would explore all possibilities.

We’ll continue to keep you updated on how these cases progress, although there’s no reason to believe that the matter will be resolved in the near future.