Final answer:
In an attack tree diagram, the task 'Apply security patch to system' would be categorized under 'Control,' as it is a security measure taken to prevent attacks. The task 'Apply security patch to system' would be assigned to the 'Control' category on an attack tree diagram.
Step-by-step explanation:
If you were to place the task "Apply security patch to system" on an attack tree diagram, it would be assigned to the category of Control. An attack tree is a graphical representation of the different ways an information system can be compromised. The task of applying a security patch is a preventative measure to safeguard the system against vulnerabilities and would therefore be considered a form of control that helps to mitigate the risk of an attack.