Daylight Saving Time ?

I am using ATIH 2014 and windows 7.
I have a lot of files (mp3 and jpeg files) that, I am sure, I have not modified.
When I launch an OnLine backup, ATIH 2014 backups these files again.
I discover that 'computer modified file date' on my computer and 'Online backup file date' have exactly a difference of one hour.
As I am living in France (I hope you understand my english) and as now time is winter time, may be this difference cames from 'Daylight Saving Time'. I do'nt know if in USA you are using DST.