The System Check will not stop

I have started the System Check and it will go on for hours without stopping.

If you are encountering such a problem then this means that your website's directory is looping into itself. Please make sure that your Joomla! installation directory does not contain any files or folders that point again (that are shortcuts) to your main installation folder or to another folder because this way your folders will loop into themselves and an infinite loop will be created. This causes a problem with the System Check since RSFirewall! checks all files recursively until it runs out of files and so it will never end.

Also please make sure that the names of your files or folders do not contain "/" or "\" (or any combination of this characters, i.e.: /folder, \file, \folder/ etc.).

And it will be best to have cache disabled on your site from Plugin Manager > System Cache and Global Configuration > System. Also delete the remaining Joomla! installation cache.