I want to warn everyone of the mantra, and of it's correct pronunciation:
"Om Aim Hrim Klim Chamundaye Vichche" is the wrong way to say it. The correct way is:
OM AING HREENG KLEEN CHAMUNDAYE VICHCHE
The way you pronounce a mantra is very crucial. Some people have accidentally prayed for insanity. In Rayayan, Kumbhkaran wanted to ask for "Indrasan" but got "Nindrasan" (though the Gods made it happen). The same accident applies to us.
The danger with this mantra is ON AVERAGE it's used more for either immediate emergency, times of war, or black magic. Generally if you want protection or removal of ghosts or negative feelings, you pray to Durga and Hanuman.
The mantra I posted above requires that the prayer have no ego, and do it with the right concentration. Chamunday is an angrier form of Durga Maya, and she will fulfill your wish but it may not be the way you expect. As well, if you have a high ego then she will kill you.
I've found this from experience by knowing people who died because of this prayer.
If you must do it, pronounce it the way I posted and have a pure heart. Seriously, I'm not joking here.