Selecting multiple objects simultaneously in the runtime with a mouse (yeah, like in all RTS)

Hi, guys. I'm planning to start a new project, so firstly I'm looking for the information about what is unclear for me by now.

The most question is the one from the headline: how to create selecting multiple objects with mouse like in all RTS. I mean pressing down the mousekey, creating rect by moving mouse pointer from the point where the key has been pressed, and after releasing the key all the specific objects within the rect between dot where mousekey had been pressed and the dot where mousekey was released should be selected.

I found discussion on the similar question: http://answers.unity3d.com/questions/8693/multiple-object-selection.html But it's nearly 7 years old. Maybe someone has new thoughts on the topic, or new instruments appeared in the Engine?