Nevertheless, in February 2008, a group of security researchers published details of a so-called "cold boot attack" that allows full disk encryption systems such as BitLocker to be compromised by booting the machine off removable media, such as a USB drive, into another operating system, then dumping the contents of pre-boot memory. The attack relies on the fact that DRAM retains information for up to several minutes (or even longer if cooled) after power has been removed. There is the Bress/Menz device described in US Patent 9,514,789 that can accomplish this type of attack. Use of a TPM alone does not offer any protection, as the keys are held in memory while Windows is running. Similar full disk encryption mechanisms of other vendors and other operating systems, including Linux and Mac OS X, are vulnerable to the same attack. The authors recommend that computers be powered down when not in physical control of the owner (rather than be left in a sleep mode) and that the encryption software be configured to require a password to boot the machine.