Section 230 of which act provides immunity to an internet service provider (isp) that publishes user-generated content, as long as its actions do not rise to the level of a content provider?

The correct answer is: Communications Decency Act.

Explanation:

The Communications Decency Act was enacted in response to concerns about the easy access to media targeted towards a mature audience on the Internet and how it affected children, as a means to regulate the content on the web. Section 230 was made to supply protection to the Internet service providers from actions against them rooted on the content of third parties.