A name with illegal characters is indeed an "illy". These names were made when b.net was a bit less restrictive, allowing for these names to be made. An example would be ~SEXICUTIONER~ (Notice the ~'s).
I do know this - xenforo dropped the ball by not keeping the vbulletin reputation comments as a feature. The loss of the Reputation comments data when we switched to Xenforo really was the death knell for the site when it came to all the users that left. I know I missed it so much and I got way less interested in the site when that feature was gone and I run the site.