Damage inside my Victoria Plums

The plums have just started to ripen on my Victoria Plum tree and as usual it is loaded with fruit but this year nearly all of the plums have some brown stuff round the stone and I have seen a tiny grub in some of them.
Does anyone know what is wrong and is there anything I can co to prevent this happening again next year

 

Plum moth. Next year you should hang a Pheramone trap to attract the males. Most Garden Centres sell them in early Spring.