I run the Temple of Assassins server and got on it Saturday morning about 9:30 am for a few frags. Then I started getting fragged/ knifed when no one was in site...happened about 4 times and I was like WTF? I noticed the invisible guy fraggin me didn't have a name, so I asked  if anyone else noticed this...(there where about 12 on the server)...no answer. Thought maybe it was my imagination, and it happened about 4 more times, so I went to the server and got status and there wasn't anyone with "no name", there was a guy named
redrum223 that had colored his name the same color as the background...this was the "invisible" guy. I asked him wtf he was doing, he laughed...the map changed, next map he had a skin...
I remember in Quake2 they came out with some anti aimbot
software that used an invisible skin called "fluffy", some cheaters found out about it and started playing with the skin making them "invisible"...thought maybe this is about the same thing...anyone else run into this?

WhiteFeather

there is an invisible skin but it only works if the server and clients have it, in ef (also q3 engion) there was a bug that some times a palyer would join and be invisible, but if it still existed we would see it alot more