If you’re running a web server on your computer, you should use a PAC file rather than the HOSTS file to block ads so you can change to a port that doesn’t conflict. By default, BlackHoleProxy uses port 3421 because it was designed to be used with the No-Ads PAC file.

Last but not least, don’t forget to clear your browser’s cache after setting up your ad-blocking HOSTS or PAC file, or the ads will be retrieved from your cash