OK, I believe I have found some relevant information on this problem. I found it on this link:
https://www.ads-software.com/support/topic/a-non-existent-page-is-showing-up-on-my-analytics/page/4?replies=126
Go to line 102
Briefly, these addresses can’t be stopped by blocking the IP address, because they’re not actually coming to your site. The aim of this type of attack is to trick Google Analytics.
Here is the explanation which I found helpful from the post cited above, courtesy of Samuel Wood (Otto) www.ads-software.com tech guy:
This isn’t a WordPress specific thing. This isn’t even specific to individual WordPress plugins. Like you said, your “personal website is CodeIgniter” and you can see it there.
Here’s a quick primer on how Google Analytics works.
So, you get setup on GA and get a code from them. The code looks like UA-number-1 or some such thing. That number is your “account number” on GA. Now, this code and a bit of javascript go onto your webpage. Now, somebody visits your page, and their browser runs that javascript code.
That javascript code is what “records” their visit. It makes their browser talk to Google Analytics. Specifically, it makes certain types of HTTP requests that Google records information about, and then GA displays summaries of that information to you.
Pretty basic, right? Still with me? Okay, now, if all it is is this Javascript sending the “visit” to them, then anybody can fake that. Anybody at all. All I have to do to make your GA show false information is to send my fake information directly to GA.
I don’t need to visit your site at all. I don’t need to run javascript at all. I just need to reproduce those HTTP requests, which are public and so anybody can see them and how they work. They’re even fairly well documented, publicly, by Google themselves.
So, now, let’s say I’m a spammer jerk. I want to get people to see my spammy site. So, what do I do? I write a small bit of code to send thousands upon thousands of these fake requests to GA, and I simply cycle through all the UA numbers, in order, at random, whatever. I send a fake visit, with a fake referrer, and my spammy domain name. And guess what? It shows up in your Google Analytics screens.
You see this spam like any other normal visit. Because as far as GA is concerned, it was a normal visit. All they’re recording are those HTTP requests, which normally come from the GA javascript code. But a request is a request, and making a fake one is very, very easy.
That is what is going on. All I need is your UA number and with only a minor bit of effort I can fake a visit to your site without ever actually connecting to your site at all. That fake visit can have any domain name and any referrer in it that I choose.
This is an attack on Google Analytics, to promote whatever site is showing up. You cannot block it on your server, because your server is not involved at all.