Because, at least in theory, it can be vastly smarter than a human hacker (or vastly smarter at specific problems, like probing for security vulnerabilities or

Because, at least in theory, it can be vastly smarter than a human hacker (or vastly smarter at specific problems, like probing for security vulnerabilities or understanding machine code.) Imagine a self-replicating botnet. Each new computer helps hack additional computers and increases the total ability/intelligence of the AI by adding computational resources. It could quickly compromise almost every connected computer.