Do you mean the SelFence command? (Rhino BETA Feature: Fence Selection and Selection commands | Rhino 3-D modeling). The Beta version has a new SelectThroughObjects option.
Or you can use SelBrush (Selection commands | Rhino 3-D modeling) which does the same thing, and is already available in v8, except that it uses a “thick” brush path instead of a thin polyline for intersection.