First off, DM doesn't just automatically start updating your device on its own when "you just plugged it in", it always asks first and makes you choose whether to update or cancel.
Now as to your problem:
If it was an update to the OS from DM(desktop manager), then there should be a backup. Try looking in mydocuments for a backup(usually a .bbb file), or just hook the device up to DM and press Device > Restore. This should give you the option to restore from the backup file DM created when doing upgrades(it will already be looking in the correct directory).