Yahoo informs Facebook of more potential patent infringements

Yahoo is said to have written to Facebook indicating that it believes that 16 patents it claims to hold "may be relevant" to open source technology allegedly being used in the data centers and servers of the social networking company, according to a regulatory filing by Facebook on Thursday.

The Internet company has not threatened or initiated litigation in connection with the matters referred to in the letter of April 23, "but it may do so in the future," Facebook said in the filing.

Yahoo filed a lawsuit in March against Facebook alleging that the company had infringed on 10 of its patents, and last month added two more patents to its complaint. "As is common in intellectual property litigation, Yahoo could in the future assert additional patent or other claims against us in this or in other proceedings," Facebook said in the filing.

Facebook denied infringing Yahoo's patents, and countered by alleging that Yahoo had infringed 10 of its patents. Yahoo claimed in a filing before a federal court that eight of the patents were acquired by Facebook in the last five months, and several were purchased after Yahoo filed the suit.

"On information and belief, many, if not all, of these patents were acquired by Facebook for purposes of retaliation against Yahoo! in this case," Yahoo said in the filing before the U.S. District Court for the Northern District of California, San Francisco division.

Yahoo claims that there is an agreement between the in-house counsels for the two companies to raise intellectual property issues with each other in the first instance.

The April 23 letter to Facebook about other potential patent infringements may be in line with the agreement.

Yahoo and Facebook were not immediately available for comment on Facebook's filing.