Messages can be protected against eavesdropping by employing a security service of confidentiality (or privacy). This security service is usually implemented by encryption.

In ancient China, it is said that to act against eavesdropping, when discussing important matters, soldiers would instead draw the characterss instead, on hands or papers.

The Canadian heroine Laura Secord is famous for having eavesdropped the plans of American army and delivered this information to the British.