Yahoo is filing a lawsuit against Facebook over patents, following through on a threat it made last month.
Yahoo Inc. said in a court filing Monday that Facebook has infringed 10 of its patents covering advertising, privacy controls and social networking.
Yahoo threatened to sue Facebook last month, insisting that the social network license its patents.
Facebook says it is disappointed in Yahoo and pledges to defend itself vigorously against what it calls "puzzling actions."
The patent claims could cast a spotlight on Facebook's vulnerabilities as the company tries to complete an initial public offering of stock this spring. At the end of 2011, only 56 U.S. patents had been issued to Facebook. That's a relatively small number compared with other big tech companies.