Modern air defence at sea doctrines call for new shipborne surveillance and tracking systems that are based on software implementations, like software-defined radar systems. This thesis contributes to investigations in the context of the ever-demanding need to forge the other side of the same coin which is countermeasures implementation for electronic protection from high range resolution sensors based again on software-defined radar concepts and principles. The first part of this thesis looks at the problem of devising countermeasures for the protection of naval targets. The second part of the thesis is focused on the amalgamation of software and radar engineering in order to increase the verisimility issues of false targets. The remainder of the thesis is then focused on further investigations in the field of computer networks warfare. The thesis concludes with the statement that the acquired Software-defined Countermeasure Systems concepts and techniques can be used in an effective and adaptable manner in order to provide deception countermeasures for both electronic warfare and computer networks warfare fields, which both are elements of the domain of information warfare.