Yahoo's patent battle with Facebook is getting nastier.
In court papers filed on Friday, Yahoo expanded its six-week-old lawsuit against Facebook to include more allegations of intellectual property theft.
Yahoo says Facebook's social network infringes 12 of its internet patents. That's up from 10 alleged patent violations previously.
Yahoo also denied allegations that it has been infringing on 10 of Facebook's patents and accused its rival of engaging in shady behaviour.
Among other things, Yahoo says Facebook violated an agreement between the companies to notify each other of possible patent infringements before filing a court claim.
The acrimony is spilling out as Facebook is preparing to raise $US5 billion ($4.84 billion) in an initial public offering of stock that is expected to be the richest in Silicon Valley history.