This visualization shows a heatmap of fraudulent email attack frequency by day of the week and hour of the day, using a color scale from light yellow to dark navy to represent increasing attack counts. The D3 v3 code renders an SVG grid with 24 columns for hours and 7 rows for days, using `d3.scale.quantile` to map values to a nine-color scheme. Day and hour labels are included, and the data comes from a JSON endpoint queried via `d3.json`, filtered through the `lect` API. The example uses React as the framework and includes a legend showing the value ranges for each color bucket.