Why are timestamps on extracted files sometimes off by an hour under Windows?
The root cause is a longstanding bug in Windows NT, Windows 95/98, and Windows CE. If an archived file was last modified during Daylight Savings Time (a.k.a. Summer Time) and is being extracted during Standard Time–or vice versa–Windows applies the current timezone offset (including DST) to the extracted file instead of using the offset that was applicable on the date the file was created or otherwise modified. This results in an off-by-one-hour problem in some extracted files, especially around April and October when locales that observe DST typically switch between it and Standard Time. (Aside: You can see the bug in action, completely independent of Zip and UnZip, by saving a Windows directory listing just before the switch and comparing it with one taken just after the switch. All file times will appear to shift by an hour.
