hover demo

<!DOCTYPE html>
<html>
  <head>
    <title>Leaflet example | CartoDB.js</title>
    <meta name="viewport" content="initial-scale=1.0, user-scalable=no" />
    <meta http-equiv="content-type" content="text/html; charset=UTF-8"/>
    <link rel="shortcut icon" href="https://cartodb.com/assets/favicon.ico" />
    
    <style>
      html, body, #map {
        height: 100%;
        padding: 0;
        margin: 0;
      }
    </style>

</head>
    
  <body>
    <div id="map"></div>
    
    
    <script src="https://libs.cartocdn.com/cartodb.js/v3/cartodb.js"></script>
    <script>

function main() {

var map = L.map('map', { 
          zoomControl: false,
          center: [43,-90],
          zoom: 5
        })

L.tileLayer('https://tile.stamen.com/toner/{z}/{x}/{y}.png', {
          attribution: 'Stamen'
        }).addTo(map);

cartodb.createLayer(map, 'https://andrew.cartodb.com/api/v2/viz/93cd9a14-4011-11e3-932f-3085a9a9563c/viz.json')
         .on('done', function(layer) {
          map.addLayer(layer);

layer.getSubLayer(1).setInteraction(true);
          layer.getSubLayer(1).setInteractivity('cartodb_id, area_sqkm');
          var infobox = new cdb.geo.ui.InfoBox({
            width: 300,
            layer: layer.getSubLayer(1),
            template: '<p>square km: {{area_sqkm}}</p>'
          });

$("body").append(infobox.render().el);

}).on('error', function() {
          cartodb.log.log("some error occurred");
        });
//begin vector hover integration
 var sql = new cartodb.SQL({ user: 'andrew', format: 'geojson' });

var marketsLayer = L.geoJson(null, { 
          style: {
            color: "transparent",
            fillColor: "transparent",
            weight: 1,
            opacity: 0.65
          }
        }).addTo(map);

sql.execute("select cartodb_id, ST_Simplify(the_geom, 0.1) as the_geom from ne_50m_urban_areas").done(function(geojson) {
          marketsLayer.addData(geojson);
          marketsLayer.on('mouseover', function(e) {
            e.layer.setStyle({
              color: "red",
  		  
			  weight: 3,
              opacity: 1
            });
          })
          marketsLayer.on('mouseout', function(e) {
            marketsLayer.resetStyle(e.layer);
          });
        });
//end vector hover integration
      }

// you could use $(window).load(main);
      window.onload = main;

</script>

</body>

</html>

Modified http://libs.cartocdn.com/cartodb.js/v3/cartodb.js to a secure url

https://libs.cartocdn.com/cartodb.js/v3/cartodb.js