creeping corruption of my jpeg. .jpg files?

I'm running windows XP and have noticed a gradual/creeping corruption of the jpg/jpeg archive from my digital camera. They've been fine on download and then despite no apparent modification, going back to the original file c.12 months later they will not load from the hard drive and invoke a "drawing failed" error in most of the graphics handlers that I've tried. I'd say this has now affected c.30% of my archive, without any obvious pattern to the corruption. It looks like a viral thing but I have up to date sophos and nothing showing on scan.

Any bright ideas appreciated
thanks
Chris

 

Have you tried the files on another pc?

 

Thanks for pointing out this very sensible sanity check. Yes, I just emailed a couple of offending files to another machine and they both loaded into MS photo editor but there was clearly an interruption to the data stream since the resulting image was blacked out for the lower 90% of its area.

regards
Chris