Tumblr now allows users to encrypt their connections with the microblogging service. The feature is only offered as an opt-in option for now. The adoption rate of HTTPS — HTTP with SSL encryption — by online services has increased rapidly over the past several years. Many popular online services are rushing to make HTTPS the default setting, or have done so already. Many users today access online services primarily from their smartphones and tablets, which are frequently connected to public, insecure and generally untrusted wireless networks.”]
Source: https://www.csoonline.com/article/2134354/tumblr-offers-ssl-option–but-not-default.html