Products
Webtrends Analytics 9.x
Cause
In January 2014, Yahoo has started moving all search traffic to secure/SSL by default. In addition to this, they are also removing all referrer information. This change will cause the traffic from Yahoo to display as Direct Traffic and it will not be included in any Search Engines, Search Phrases, or Search Keyword reports.
More Information
More information on this topic can be found here: http://blogs.webtrends.com/2014/02/yahoo-and-bing-roll-out-secure-search-functionality/