SAN FRANCISCO (Reuters) - Yahoo Inc last year secretly built a custom software program to search all of its customers' incoming emails for specific information provided by U.S. intelligence officials, according to people familiar with the matter.<div><a href="http://feeds.reuters.com/~ff/reuters/technologyNews?a=826Z7v5xgKw:1WH4Zes7uos:yIl2AUoC8zA"><img src="http://feeds.feedburner.com/~ff/reuters/technologyNews?d=yIl2AUoC8zA" border="0" /></a> <a href="http://feeds.reuters.com/~ff/reuters/technologyNews?a=826Z7v5xgKw:1WH4Zes7uos:V_sGLiPBpWU"><img src="http://feeds.feedburner.com/~ff/reuters/technologyNews?i=826Z7v5xgKw:1WH4Zes7uos:V_sGLiPBpWU" border="0" /></a> <a href="http://feeds.reuters.com/~ff/reuters/technologyNews?a=826Z7v5xgKw:1WH4Zes7uos:-BTjWOF_DHI"><img src="http://feeds.feedburner.com/~ff/reuters/technologyNews?i=826Z7v5xgKw:1WH4Zes7uos:-BTjWOF_DHI" border="0" /></a></div><img src="http://feeds.feedburner.com/~r/reuters/technologyNews/~4/826Z7v5xgKw" height="1" width="1" alt="" />