Which type of threat actor is most likely responsible for a series of unsuccessful attempts to gain unauthorized access using publicly available tools?

The most likely threat actor responsible for a series of unsuccessful attempts to gain unauthorized access using publicly available tools is an unskilled attacker. This type of threat actor typically lacks advanced skills or sophisticated techniques, relying instead on easily accessible resources and methods to carry out their attacks.

Since they are unskilled, their approach often involves trial and error, which can manifest as multiple unsuccessful attempts. This behavior reflects a lack of experience and knowledge about more effective hacking techniques or the security measures in place, leading to a reliance on basic tools and information they can find online.

In contrast, advanced persistent threats (APTs) and state-sponsored hackers are generally characterized by their sophistication, targeted methods, and resources to achieve their goals. Insider threats involve individuals with legitimate access to systems who misuse that access, which is distinctly different from an unskilled attacker attempting to breach security from an external position.