Whats all over my Acer?

Hi all

Could anyone tellm me what is this all over my acer Japanese Maple? Is it harmful and how to deal with it?

 

Looks like a scale bug, I had some on my magnolia but didn't use anything I just scraped them off, none have returned but i do keep checking, I am still a novice but I'm sure someone with more experience will be along shortly with advice on any chemical solution.

 

I do not think your acer will tolerate its company for long without starting to show signs of suffering.
Hang on, somebody will know what it is and what you can do - before the night's out,