Right, after taking a look at the files I find that it is not just the dpi that has changed. It has also changed the the size. What was 2832 x 2128 is now 2048 x 1536. This is not too bad for most images because they only need to be printed at 8 X 10 but some of the larger images were left like that because I needed them printed in a larger format on canvas (custom job I am doing for gallery) I'm not talking 1 or 2 pictures here, there are hundreds that are affected. The issue is not that I have to now change the dpi, some of the images will not be the right size for printing and to enlarge the images could cause additional problems (I do have backups). The problem is something has changed this on all image files without my knowing. If it has done it once, then what will stop it doing it again? If I was not so paranoid and did not have everything backed up I would really be up that creak without my paddle. Thanks to all that have contributed. I have no problem with changing dpi etc.. I do have a problem with my machine changing things without my knowledge. As I have mentioned before, I do teach people to use computers and one of my main packages is Photoshop so I do know about resolution and dpi. When you work on your personal computer with exactly the same software set up as your work computer and only the files on your personal computer are effected even though you have done the same things, then something somewhere is wrong. The only difference is that my personal PC is only using the standard microsoft firewall and Symantic AV. It just seems strange that it just the image files, I have been looking around the usual support groups for any particular viruses but up to now have not found anything with the same symptoms, hence my post here, all I was doing was trying to find out if anyone else has had the problem. I do not think it is a virus, just exploring that to rule it out.