Yahoo has given users of its webmail service the option of using an SSL connection for their sessions. The HTTPS option is not enabled by default, but users can turn it on with a couple of clicks. Google enabled HTTPS-only by default for its Gmail users in 2010, just after company officials disclosed that Chinese attackers had penetrated Google and several other companies as part of a targeted attack campaign. The move by Yahoo is an important step toward providing Yahoo Mail users with more security on their accounts.
Source: https://threatpost.com/yahoo-makes-ssl-option-available-mail-users-010813/77376/