It's just debris in the COR1 detector. It's always there, you just can't always see it in the processed versions of the images. In fact there are more donuts in the image that you don't see even in that processed image. They look like donuts because they're completely out of focus and therefore take on the shape of the optics (it's got a central occulting disc to block the sun). You can always see them in the raw versions of the images (ALWAYS look at the raw fits files).

Here's what a raw COR1-B image looks like from 2009 (minimal processing, only levels adjusted prior to conversion to JPG, no other changes):
[link to imageshack.us]
Here's the one from the 17th:
[link to imageshack.us]
See those donuts at the bottom left? They're not quite in the same spots because the final processed JPGs everyone looks at are rotated a bit to maintain a consistent reference frame. The raw fits files are, of course, unrotated.