Their ‘message’ claims that no images were hurt in the process, but I have no clue what ImageShack will be able to recover, if anything. So hopefully our members have copies of any images that have been replaced. Here is a thread on their forum where multiple people report the issue. If the latest report there is correct, your images at ImageShack have been renamed, and new images with the ‘message’ have been put in their place. So you should be able to delete these and revert your images.
Note: The only result of this ImageShack hack is the replacement of images. Currently, I am not aware of any way that an image can be used to harm your computer.
Let me know if you have any questions or concerns.
— MordEth