What makes an electronic communication line secure or non secure?

Question

Radio waves are free right (literally)? How can free floating signals have security? Even hard lines can't be protected to the point of being titled "secure". Right?

Answer 1

Communications lines, be it over cables or radio waves, transfer intelligence and data by means of modulation or encoding.  When standard means of modulation or encoding is incorporated, then anyone who has equipment capable of demodulating or decoding the communications information will be able to listen-in or capture and record the data.

Security, is generally only possible when the lines of communications, be it cables or airwaves, is "Encrypted" with a highly secure encryption algorythm.

When encrypting digital data with AES (American Encryption Standards) 128 or 256 bit encryption, it is "currently" virtually impossible to intercept and decode the data.