How to avoid Copy Paste in input fields

Here is a code to avaoid 'Ctrl+V' use by the users on field that you want to enforce double validation on:

function KeyPressed(e) 

  { 

    var evt = typeof window.event != 'undefined' ? window.event : e; 

    var val = evt.keyCode == 86; 

    if (evt.ctrlKey && val) 

    { alert(evt.ctrlKey +", "+ val);

      if (evt.stopPropagation) 

      { 

        evt.preventDefault(); 

        evt.stopPropagation(); 

      }

      else 

      { 

        evt.cancleBubble = true; 

        evt.returnValue = false; 

      } 

  } 

crmForm.all.firstname.attachEvent("onkeydown",KeyPressed);