After Yahoo sued Facebook in March for patent infringement, the social networking site fired back earlier this month with a countersuit claiming that Yahoo is infringing on ten of Facebook’s patents, the Daily Business Review reports.

Facebook alleges that Yahoo is violating patents covering services such as its homepage, content optimization, relevance engine, photo-sharing service and advertisements displayed throughout the site. Facebook’s own engineers allegedly invented three of these patents, and another was co-invented by Mark Zuckerberg himself.

This is not the first time Facebook has battled over patents. In 2008, Leader Technologies Inc. sued Facebook, alleging the company infringes a patent on its data management tool. The case went to trial in Delaware district court in 2010, the first time Facebook had ever faced a jury. The jury found Facebook had infringed the patent, but it also invalidated the patent because Leader had sold the technology before seeking patent protection. Leader appealed the ruling to the U.S. Court of Appeals for the Federal Circuit, which heard oral arguments in March. The court has not yet issued an opinion.

Facebook’s countersuit can be found here.