Support

You need to talk to your host. They have set up Apache incorrectly. Namely, the virtual host entry for your site is the first virtual host entry Apache loads. Moreover, Apache does not have a catch-all, default virtual host.

What happens is that the sites whose domains you see used to be hosted on the same server as you. Somewhere out there there's a stale DNS record pointing that domain to the same IP address as your server. Therefore someone's computer tries to hit the server your site is hosted on to retrieve that site that's no longer there.

On a correctly installed Apache there's a default, catch-all virtual host which returns an error quickly and is done with it.

On your server, the host never bothered to do that – probably because they thought they can simply leave the default cPanel installation intact. Since the first virtual host Apache loaded was yours all that junk traffic ends up on your site.

Apache sets the HOST environment variable to the hostname it has received in the request. Joomla reads that on every request and uses it for constructing URLs. This is a good feature; it is why you can serve the same Joomla installation from different domain names without having to redo the site from scratch.

The problem is a simple omission on the part of your host. Tell them to fix it. It's not a big deal and can happen to everybody – we even saw that in one of the big name hosts we're using ourselves.