An intellectual-property war between two of America’s tech giants is heating up as Yahoo added two more patents to its suit against Facebook on Friday. “Today’s filing underscores the breadth of Facebook’s violation of Yahoo's intellectual property,” a Yahoo spokesman told reporters. The suit was first filed last month, and Facebook immediately countersued. Facebook has escalated its efforts to stockpile patents recently, snatching up $550 million in AOL patents, as well as hundreds of IBM patents. Yahoo says Facebook broke an understanding that the companies would talk over infringement issues before taking them to court.