At work, somebody had Kazaa installed on a workshop PC. It had been used for years with no problem. Then a new employee swans in and installs and uses E Mule. 3 days later we have no internet connection anywhere in the building. Our provider had cut us off for being in breach of their T&Cs. It was sorted, E mule was removed, internet restored and new employee slapped about for messing with the system.
I think that E mule is detectable while Kazaa is not.