function disableCtrlKeyCombination(e){  
  var forbiddenKeys = new Array("a", "c", "x", "v");
  var key;
  var isCtrl;

  if(window.event) {
    key = window.event.keyCode;         //IE
    if(window.event.ctrlKey) {
      isCtrl = true;      
    }else {
      isCtrl = false;
    }
  }else{
    key = e.which;                     //firefox
    if(e.ctrlKey||e.metaKey) {
      isCtrl = true;      
    } else {
      isCtrl = false;
    }
  } 
  
  if(isCtrl) {            
    for(i=0; i<forbiddenKeys.length; i++) {      
      if(forbiddenKeys[i].toLowerCase() == String.fromCharCode(key).toLowerCase()) {  
        return false;
      }
    }
  }
  return true;
}