Can Web Workers utilize 100% of a multi-core CPU?

This uses 100% on my 2500K:

var code = "while(true){}";
var URL = window.webkitURL || window.URL;
var bb = new Blob([code], {type : 'text/javascript'});

code = URL.createObjectURL(bb);

new Worker(code);
new Worker(code);
new Worker(code);
new Worker(code);

http://jsfiddle.net/MTJ27/81/