Kicked from Server?

[SEE]

I have only been on MP using HL for a few hours and have a standard V4.09 installation with no mods, etc. I joined a server and was surprised (and disappointed) that for some reason I have been kicked from it and it no longer shows up on HL. All I can think of is, that during one session, a message came up saying that 'Cheating has been detected' (several times) but I assumed this message referred to another player as I was flying the plane in the normal way I would in SP mode.

Unless there is another explanation I don't understand why I would be kicked off or what constitutes cheating. May be someone could offer a reason or give advice.