Although details are still appearing, Sophos is reporting that a particular combination of circumstances can result in FileVault passwords being exposed in plain-text log files. The combination is somewhat unlikely — the Mac had to be using FileVault 1 under Mac OS X 10.6 Snow Leopard, be upgraded to 10.7 Lion, and then updated to 10.7.3, all without switching to FileVault 2. Nevertheless, if this applies to you, change that password! follow link
Find Your Mac's Serial Number
Want to check your Mac's serial number quickly and easily? Select About This Mac from the Apple menu, and click on the text directly below "Mac OS X" that reads "Version 10.x.x." Click once and you'll get a build number which is more specific information about the software. Click twice, and you'll get your Mac's serial number.
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FileVault Passwords Potentially Logged in Plain Text