The company also accused Facebook of not having a good-faith belief in the counterclaim it filed almost a month ago.
“Today Yahoo! filed additional claims against Facebook in U.S. District Court related to two additional patents on which Facebook infringes," Yahoo said in an emailed statement.
"As we have stated previously, Yahoo!’s 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. We intend to vigorously protect these technologies for our customers and shareholders.”
In the face of the new claims, Facebook was more succinct: "We remain perplexed by Yahoo's erratic actions," a Facebook spokesperson said, also in an emailed statement. "We disagree with these latest claims and we will continue to defend ourselves vigorously."
With the "erratic" dig, Facebook seems to be depicting Yahoo as the tech-company equivalent of a crotchety old man. Considering Yahoo specifically calls out Facebook for using recently acquired patents as the basis of its lawsuit -- even though some of the patents in Yahoo's claim were acquired as well -- the image may well stick.
A quick recap: Shortly after appointing former PayPal executive Scott Thompson as CEO, Yahoo warned Facebook that the social network was infringing on its intellectual property -- specifically, 10 patents that relate to Internet technologies.
It then went ahead and sued Facebook a few weeks later, becoming something of a tech-industry pariah in the process.
Facebook, rather than try to end the suit with a quick settlement, set out to arm itself for a retaliatory strike. The social network quickly acquired many patents from both IBM and Microsoft. Facebook also countersued Yahoo -- saying that it, too, was guilty of patent infringement.
The whole affair would be funny if it wasn't a symptom of a wider, all-out patent war. In the last year we've seen Apple, Google, Microsoft and a host of others sue the pants of each other, and a company that barely does anything can claim to hold a patent on the web itself.