Very similar, I remember this is how AOHell did some of its tricks.

I remember before AOL’s standalone Instant Messenger became popular, mid-1990s, we could go into AOL chat rooms (and Yahoo’s) and throw inline HTML tags into the chat box, and they’d affect everything below them until we either sent a closing tag, or enough posts came through to finally push it off the top of the screen. It’s kind of wild how long it took them to implement even very basic protections.

There were some punters that would need a single IM, although I don’t know the exact method, I am pretty sure it was malformed rich text or html.

I think most punters sent large amounts of data in many consecutive IMs and hid the local modals so they didn’t punt themselves.