"In a paper published in 2008 and focused on the then latest version (v5.1a) and its plausible deniability, a team of security researchers led by Bruce Schneier states that Windows Vista, Microsoft Word, Google Desktop, and others store information on unencrypted disks, which might compromise TrueCrypt's plausible deniability. The study suggested the addition of a hidden operating system functionality; this feature was added in TrueCrypt 6.0. When a hidden operating system is running, TrueCrypt also makes local unencrypted filesystems and non-hidden TrueCrypt volumes read-only to prevent data leaks. The security of TrueCrypt's implementation of this feature was not evaluated because the first version of TrueCrypt with this option had only recently been released."