Did this all happen in the same server?

I'm guessing this is the work of the server whoever was hosting that...

To explain what I bet they did is that they editted the names of the people who would enter the server. Now, anyone who joined after the names were editted for the server would see a different name than the person originally had since the server would be sending an editted version of the user name list to the joining client. So, it would also explain why no one else had a different name, but all of the other names were changed. If what I'm thinking is right, it is no virus, just the server messing around changing memory values.