A. Essentially, the BitLocker encryption that is part of Vista Enterprise and Ultimate editions takes effect only if the machine is actually shutdown (e.g., powered off, including shutdown or hibernate). If a machine is placed in sleep mode, then upon waking, BitLocker checking isn't performed (e.g., no USB key is required for disk access). To elevate this security, administrators are advised to set machines to hibernate after a short period of time when in sleep mode