“We received a letter dated April 23, 2012 from Yahoo indicating that they believe 16 patents they claim to hold may be relevant to open source technology they allege is being used in our data centers and servers,” the document said.
“Yahoo has not threatened or initiated litigation with respect to matter described in this letter but it may do so in the future.”
It said Yahoo! had already filed a lawsuit in the US District Court for Northern California alleging a number of Facebook product infringements, in particular 12 patents relating to advertising, social networking, privacy, customization and messaging.