hectorm/hblock ? reverse-engineered prompt

Build me a small command line tool that helps protect my computer by blocking ads, trackers, and malware domains.

I want it to work from the terminal, pull together domain lists from multiple sources, and generate a hosts file that my system can use to stop those sites from connecting. It should be safe enough to use on a real machine, so please include a clear warning about backing up the existing hosts file before replacing anything, and give me a way to generate the file without blocking anything if I need to temporarily disable it.

Make it easy to install and run, with helpful usage text and a few options for different output formats if that makes sense. If you can, also add a simple way to keep the block list updated automatically over time. Keep it lightweight and compatible with normal POSIX shell environments, and look up current docs online if you need to.