Tar file within a file?

[Ben <ben skyrock co uk>]

I recently discovered on one of our websites running off a machine 
installed with RH7.1, an image file that should be 400bytes but was 
actually 200mb+. When I examined the file it turned out to have a tar 
file from one of the automated backup processes tacked onto the end. 
If someone viewed the page with that image on, they would see the 
correct image, but if that file was downloaded from an apple mac, it 
would also download the 200mb file as well, giving that person the 
whole contents of our site.
Does this sound like a sneaky hacker trick or is this some kind of 
file error (we did run out of disk space once recently)

Thanks in advance.

Ben