Intruders have extreme flexibility in attacking and controlling a target. They are free to pick the victim, the time and nature of the attack, the means of command and control (if desired), and many other variables. Asymmetry of interest in gaining and retaining control is more important to attackers than defenders. Microsoft security chief: In some respects the fight against online criminals is not a fair one. The attackers have all the time in the world, the cooperation of other hackers and a virtually limitless number of potential targets.”]
Source: https://taosecurity.blogspot.com/2007/04/threat-advantages.html