The Spark core does HTTP but not HTTPS, so the data you send to or receive from a host over the Internet over HTTP is visible to anyone looking in.
But the Spark core does have a secure connection to the Spark cloud, so depending on what you want to do, that may be the best option. There is a feature in beta right now that lets the Spark cloud server act on your behalf with other Internet hosts over a typical HTTPS connection.
So the flow is your core talks to the Spark cloud which then talks to an website on your behalf. As you might imagine, you might have to give the Spark cloud your credentials to the other website in some manner (OAUTH would nice!) so it can act as your agent.
Maybe you should explain more concretely what you are trying to do so we can suggest a way to do it?