There was a time when the web was open. Communications taking place on the early web were not masked in any significant fashion. This meant that it was fairly trivial for a bad actor to intercept and read the data being transmitted between networked devices. To address the risks of transmitting such data over the web, traffic encryption was invented. Today more than half of all websites use HTTPS. In fact, according to data obtained from Cisco Cognitive Intelligence, the cloud-based machine learning engine behind Stealthwatch.”]
Source: https://blogs.cisco.com/security/threats-in-encrypted-traffic