If you find the following in the error.log of an apache webserver:
… [error] [client XXX.XXX.XXX.XXX] client sent HTTP/1.1 request without hostname (see RFC2616 section 14.23): …
You can be sure that in most cases it is a computer, largely even running a webserver and many other services, with no firewall, lacking security precautions, xampp and phpmyadmin open to everybody, empty passwords, etc. sometimes they have all of these features at once. I have not checked for viruses but I expect most of them to even be infected or at least hacked and working for someone else than they ought to.