indian jasmine

hi
thank you very much for the previous replys. i have an indian jasmine flower plant. it is doing well. as it is snowing i kept it inside the house near a window. today i just observed that many leaves had black spots on the back side of the leaves.and also some light brown deposits.i cant understand whether these deposits are insects or some kind of plant material.this is my favourite plant. please do give me some advice on how to get rid of this spots.and please do tell me why this spots occur.
and if this is harmful to the plant.
any suggestion would be helpful.
thank you,
vasavi