Thats easy to answer James, MCS has a small problem that allows people to abuse it and they have done, used sensibly it presented no problem.
The later versions of MCS didnt have the flaw just the early ones and its been an uphill struggle lasting a few years to get some hosts mainly Italian rooms to stop abusing it.
I would rather not repeat what the flaw is, no point in allowing more idiots to take advantage of it, but it is the code base for many of the current servers so its not a problem with the flaw fixed in my opinion.
KM who made the program some years ago joined with me in asking folks not to use it and released a much improved chatserver, the WCS you know today, its funny that some people complain about MCS but forget without its creation we would not have any of the broad range of coloured chat servers as we do today RCMS being the only tool that added extra functions to the chat rooms at that time.
I hope that info helps you understand why we do not advise its use or distribution, let an old dog die, its served its purpose.