There were using a secure system, but not as secure as it should have been. It is a commercial service, ironically like Hillary Clinton's use of a private email server. If a "secure" service is in public use, you have to accept that it can be, and has been, hacked. In this case, the people involved (except the journalist) are stupid or ideologically blind, which in many ways is worse. These people are in charge of the world's largest nuclear arsenal. Something that tempers Putin's behaviour but not the current Trump led destructors.