Possible Dead Spots on the ist d* ccd

I have noticed some black spots on some of my pictures particularly sky shots. I have carried out a quick test using white papaer and two lens, the standard 18-35 mm and a 28-90 sigma lens both show the dark spots.A friend of mine has the same camera and has taken his back to Pentax. Has anyone else had this problem.
Chris24

Why not try a test for dead pixels using
http://www.starzen.com/imaging/deadpixeltest.htm

Also, use a puffer to make sure that there is no dust on the ccd.

I am getting the same, but thought it was dust and was going to figure out how to clean it sometime. Did not think anything other than that.

Many thanks to those who have responded, my conclusions are that it is dust and I am about to order the large puffer from 7dayshop as suggested. I have used the test soft ware I have to say that I would like a little more info on how to interpret the results. Mine only showed results on the fastest shuter speed as recommended by the software suppliers
Chris24