Prevent execution of parent event handler

I have a tree of divs:

<div id="a" onclick="func">
    <div id="b" onclick="func">
         <div id="c" onclick="func">
         </div>
    </div>
</div>

When a click is made on a div it makes it's children invisible - ie click on "a" will turn "b" and "c" invisible.

function func{
   if ($(childId).hasClass("visible")){
    $(childId).removeClass("visible");
    $(childId).addClass("invisible");
}

The problem is: a click on "b" will call "a"'s click and make "b" and "c" invisible. How do I disable the click on "a" using jQuery?

thanks