At which of the following levels of robustness in DRM must the security functions be immune to widely available tools and specialized tools and resistant to professional tools?

Level 2 robustness is typically less stringent than Level 1, offering resistance to some specialized tools but not necessarily immunity to all widely available or specialized tools.

Level 4 is not a standard or commonly recognized robustness level in most DRM classifications for this specific description; DRM robustness models usually describe a descending scale, often starting at 1 or 0 for highest.

Level 1 robustness, as typically defined in DRM contexts, signifies the highest level of security. At this level, the security mechanisms are designed to be immune to common and specialized hacking tools and resistant to sophisticated professional attack methods, ensuring strong content protection.

Level 3 robustness implies a lower security posture compared to Level 1, offering less resistance to various hacking tools and methods.