Hi, developer here! By "not secure", I'm guessing you mean the fact that the website isn't served over HTTPS, which would give it a little padlock icon in the address bar. You're quite right that it would be ideal to do that. Unfortunately, as with a lot of problems with ACC, the root cause is that the site is very old and runs on an antique server that is usually pretty intractable to tinker with, so it's taken a long time to do anything about. It is something that will be solved in the near future with our "ACC 2" project to recreate the site from scratch, which you might have seen recent announcements about.
There are a couple more technical details in this thread
Let me know if you have any other questions.
There's no place like 192.168.0.0/16.