How do I select Gus's right-hand vertices only?

I’m running through the Gingerbread man animation tutorial. I’ve reached the stage of Skinning and need to select the skin vertices to and assign them to the relevant vertex group (ie. Arm.R vertex group needs the right-hand vertices on the mesh).
However, whenever I ‘border select’ some vertices, either on the left or the right, mirrored vertices also automatically selected. Eg. if I border select the vertices on the right hand, the left hand vertices are also selected at the same time.
I keep reading back through the tutorial to see if I’ve missed anything, and I probably have, but I cannot find out what?

Any help gratefully received.


You still have Mirror modifier not applied.
Shift-d duplicate object and m move to another layer to have backup. Then click Apply button on Mirror modifier.

Got it. I didn’t apply the mirror modifier.