In digital rights management, the level of robustness depends on the various types of tools and attacks to which they must be resistant or immune. Which of the following types of tools are…

Hand tools are generally inexpensive, commonly available, and do not require specialized skills for basic use, making them an unlikely descriptor for sophisticated DRM attack tools.

Widely available tools contradict the 'not easily available' criteria stated in the question.

Specialized tools are a close option, but 'professional tools' more accurately captures the full set of characteristics (expensive, skill, not easily available) in the context of advanced attacks, implying a higher level of sophistication and resource investment.

Professional tools, in the context of DRM robustness, are typically expensive, require specific expertise to operate, and are not readily accessible to the general public. These tools often involve advanced hardware or software used for sophisticated attacks against DRM systems.