If you've ever used Windows Live Photo Gallery, you may have noticed that the "last modified" time of some of your movies have changed. This is caused by Photo Gallery adding an Alternate Data Stream[a] to each file: TOC.WMV:$DATA. The main file data stream itself remains unchanged, and the movie clip itself is not modified at all.
If you use Vista or later: Open a command prompt, cd into the right directory and type dir /R. You will get something like the following:
Directory of C:\Archive\Photos\2009\200910\20091031
2009-10-31 17:16 12 110 728 200910311145-CIMG6965.AVI
64 200910311145-CIMG6965.AVI:TOC.WMV:$DATA
2009-10-31 12:56 17 493 464 200910311156-CIMG6966.AVI
2009-11-01 19:58 2 270 240 200910311510-CIMG6967-0.AVI
2009-10-31 16:10 3 643 096 200910311510-CIMG6968.AVI
2009-10-31 16:12 36 923 176 200910311512-CIMG6969.AVI
2009-10-31 16:18 6 465 592 200910311518-CIMG6970.AVI
2009-10-31 16:25 19 265 800 200910311525-CIMG6971.AVI
2009-10-31 16:40 28 849 272 200910311540-CIMG6972.AVI
8 File(s) 127 021 368 bytes
Here we see eight avi files, one of which (200910311145-CIMG6965.AVI) has an ADS added by Photo Gallery.
1. Why Is This Bad?
Adding an ADS means that the file time is updated, which causes havoc in backups. It is also just bad form for a Digital Asset Manager such as Photo Gallery to modify the assets it is managing in any way without clear consent from the user.
2. What To Do About It
First of all, unless it is a problem for you, it's not a problem. The alternate data streams added by Photo Gallery are totally harmless. The only bad thing about them is the interference they cause with backup routines and other programs that rely on accurate timestamps. If you don't have any backup routines, this will not affect you - your problem is that you have no backups.
If you find your movie clips littered with ADSs hanging off them, don't worry. You can use a tool like ADS Spy[b] to remove them.
To keep them from coming back, you may want to try out the Windows Live Essentials beta[c] version. As every beta, you never really know if the beta sticker is there because it is really in development and unstable, or if it is just marketing.