a hacker scans hundreds of ip addresses randomly on the internet until they find an exploitable target. what kind of attack is this?

That scenario is describing a scanning attack , more specifically an active network scan of IP ranges (IP block scanning / reconnaissance).

In cybersecurity terms, what the hacker is doing is:

• Randomly probing many IP addresses on the internet
• Looking for systems that respond and reveal weaknesses (open ports, vulnerable services, etc.)
• Using automated tools to quickly identify exploitable targets

This falls under active scanning / reconnaissance , and is often categorized as a port/IP scanning attack that precedes other intrusions.