Who is the most likely threat actor if a website is defaced with messages denouncing the company's policies?

The most likely threat actor in the scenario of a website being defaced with messages denouncing a company's policies is hacktivists. Hacktivists typically use their skills for political or social causes, often targeting organizations that they perceive as unethical or harmful in some way. The act of defacing a website to communicate their discontent with a company's policies aligns with their motivations to raise awareness and provoke change regarding specific issues.

Hacktivism often involves publicly shaming or drawing attention to a cause, making the act of altering a company's website with opposing messages a common tactic employed by these actors. The intent is not necessarily financial gain but to promote a particular viewpoint or protest against specific actions of the organization.

The other options do not reflect the motivations typically associated with hacktivism. Corporate spies usually operate for competitive advantage or financial gain; insider threats might involve employees with access to sensitive information but are typically more concerned with data theft or sabotage rather than public protest; while malicious outsiders may have various motives such as financial gain or chaos, their actions are less likely to be focused on political or social ideals as seen in hacktivism.