A long time ago (windows 98 I believe) my screen went blank and green text appeared saying "Hello, how are you?" I was about 12 at the time so I had no idea what was going on. I don't recall my response, but I remember the "person" on the other side saying "You left a back door open. Would you like me to close it?" I restarted my computer and I still have no idea what it was.

Was this a virus, a hacker, something else? I completely forgot about it until this thread.